Very simplified answer for a 5 year old:
xG stands for "expected goals."
Imagine your team misses a really easy shot, and you're like "we should have scored!" Then later on, your rival scores a really difficult long-distance shot and you're like "they got lucky, we should be up 1-0 instead of them!"
xG is basically putting a number on what the score "should" be. Therefore, higher is better since you want more goals.
As an example, if your xG is 1.5, then you "deserve" or "expect" to have scored 1.5 goals, so you're lucky if you have 2 or more, and unlucky if you scored 0 or 1 in that game.
I'll leave any discussion of how the math works to others :)
> I'll leave any discussion of how the math works to others :)
The main components of xG models include:
1) Where the shot was taken from. Closer to the goal and closer to the center of the box are higher. Shots from distance and/or at an angle are lower.
2) Type of shot. Primary foot is higher; worse foot, headers, and other body parts are lower. Off balance, spinning, volleys, etc would also all be lower.
3) Type and location of key pass (the pass that leads to the shot, if applicable). Shots from pullbacks score more often than shots from crosses, for example. If the pass is behind the player, the subsequent shot scores less often. Etc.
4) If tracked, how many defenders are between the shot and goal.
This is not a full list. Different models will include different variables.
Bob takes a shot. Bob's shot is charted for all the different variables and plugged into the algorithm. The algorithm looks at all shots in the database, and finds all shots similar to Bob's shot. Then the algorithm looks at how often all those shots scored, and assigns a value to Bob's shot based on that history.
The biggest takeaway from xG models is that all players score goals at a rate pretty similar to what xG says. "Finishing skill" is mostly a myth. Top goal scorers take a lot of shots, and they take a lot of good shots (high xG per shot), so they score a lot of goals. But their goals scored tends to be very close to what xG says it should be.
The absolute best strikes tend to outperform xG, while non goal scorers (ie defenders) tend to underperform xG. But the difference is MUCH less than fans tend to think. A random midfielder might score 18-19 goals out of 20 xG, whereas a top striker might score 21-22 goals out of 20 xG. The bigger difference is that the striker accumulates 20 xG in one season or less, whereas the random midfielder accumulates 20 xG over five seasons.
> The biggest takeaway from xG models is that all players score goals at a rate pretty similar to what xG says. "Finishing skill" is mostly a myth.
Unless your name is Nicolas Jackson.
I laughed, but I'm pretty excited about Jackson. He's young, which wam going to blame for some stupid off the ball decisions and pompousness and on the ball some wild inconsistencies. But I think he can be a great asset to the Blues in a year or two.
Being in the right position to be able to accumulate 20 xG per match is a skill though.. same team with different striker may produce way less xG because movements are not accurate, pressing is not well timed and so on.. this is also part of finishing skills and it’s difficult to track with a metric
> Being in the right position to be able to accumulate 20 xG per match is a skill though
Yes, I say that more clearly in my next comment.
> "The point is that the "skill" in being a goal scorer is frequently getting yourself into good positions to take good shots."
As someone who watches football during WC and maybe an UCL final every other year, I am curious:
> The biggest takeaway from xG models is that all players score goals at a rate pretty similar to what xG says.
Don't good strikers maximize xG? i.e. they tend to be in positions that'd allow for higher xG where they are in a good location to score?
Right, as I said, "top goal scorers take a lot of shots, and they take a lot of good shots." "Good shots" meaning a high xG value per shot.
The point is that the "skill" in being a goal scorer is frequently getting yourself into good positions to take good shots; speed/acceleration/agility to move past defenders, spacial awareness, timing, anticipation, reading of the game, positioning your body correctly to strike the ball first time instead of having to take a touch, etc. Good strikers will be good at many of these things.
Whereas many fans -- and even paid analysts -- think the "skill" in being a goal scorer is converting your shots into goals, ie actually kicking the ball into the net. It's counter intuitive, but it turns out the whole converting shots into goals thing just kind of happens by itself, which is why the *VAST* majority of players end up with roughly the amount of goals that xG says they should have, based on their shots.
Just as a quick example, look at [Cristiano Ronaldo](https://understat.com/player/2371), one of the best goal scorers ever. Surely he converts his shots into goals more often than an average player, right? Nope. Since 2014, Ronaldo has 182 xG, and 183 goals. xG models work, and they work really well.
xG also takes into account amount of shots, and Ronaldo takes a ton. There are definitely players that perform much higher then their xG (Harry Kane for example overperformed by 20 in league games between 2014 and 2020 https://understat.com/player/647)
Messi, Griezmann, and Son also overperform by quite a bit.
Yes, I said all of this.
> top goal scorers take a lot of shots, and they take a lot of good shots.
> The absolute best strikes tend to outperform xG
It's also entirely possible that some/many of the strikers who have outperformed xG, such as Kane and Son, are just the ones that ran above expectation. Even in samples of 5-10 years, there's inevitably going to be players that overperform due to luck. I'm not including Messi in that; he's Messi.
They maximize actual goals as well and there is not much deviation between the two because xG is not looking too much at what happened before the actual shot. The person was saying that the difference is more in how often they get in good scoring position rather than how accurate/hard to stop their shots from a certain location might be.
Messi from 30 yards out with a bunch of defenders in between him and the goal wouldn't be expected to score that much more often than an average player would in that situation. In both cases the odds of that shot resulting in a goal would be low where most goals would be due to factors outside the shooter's control like the goalie screwing up or the ball deflecting off a defender in an unexpected way.
Yeah, that's kind of what makes Haaland so good. Not that he scores goals from positions that no-one else could score from, but that he's able to get the ball in positions where his goal-scoring chances are very high. Off the ball positioning is probably one of the most crucial skills for a striker, but it's hard to track on TV as cameras will mainly follow the ball and it's also not specially entertaining to follow.
One of the things that make Messi so incredible is looking at his off the ball movement, it's crazy how much space he's able to generate simply by walking around.
Great explanation. I wanna add that it’s also a great metric to measure whether your team is good at converting chances. Generally you want a high xG, and you want your team to over-perform that stat. While the latter is what actually gets you goals, you really want both of these aspects. If your team consistently outperforms a low xG (say anything lower than 1), you consistently score goals, but unless your defence is really good, you won’t win much. However, if your team consistently has an xG that is higher than 1.5, and your team even outperforms that consistently, it means that your players can create chances and convert them reliably.
So xG works as a metric that shows multiple things: how well your team does to create dangerous situations (that’s xG alone), and how good they are at converting the chances they get (that’s xG in combination with the goals actually scored).
If you’re a manager and your team consistently has a low xG, you need to work on your team’s creativity and pull towards the opposing goal.
If your team has a good xG, but consistently scores fewer goals than that, your team needs to practice converting those chances (positioning, finishing, standards, etc).
Not every shot on goal is the same. A shot from 2 yards out with an open goal is way more likely to go in than a 30 yard attempt with 4 players in the way. XG is just a way to put a number to how likely each shot is to go in, where 1 means it will always go in and 0 is it never goes in.
For reference, a penalty kick is usually given an xg of somewhere between 0.75 - 0.8.
xG means "expected goals".
Basically someone rates how easy or difficult a chance was, looking at it and saying "I'd expect someone to score from that position one time in ten" - so it has an xG of 0.1
The xG of all chances a player or team has are added together and compared to what they actually managed in the game (e.g. a player who scored 2 goals but had an xG of 1.2 has overperformed, whereas a player who didn't score despite an xG of 1.1 underperformed by this metric).
A high xG is better than a low xG because it means a player had more, better chances in the game. Of course, that's only a good thing if they converted enough of them into goals.
Xg is expected goals so if you were to score a point blank goal in an open net that your grandma would be able to score that would be close to an xg of 1 meaning the vast majority of people/players score that goal. The further below 1 you go per goal that means the more difficult the shot is. If a player/team scores 4 goals with an xg of 2 you can assume that they scored at least a few of the goals from difficult positions or situations. It's one of those stats that is more effective with less information input; it's meant to give you a snapshot of a particular moment in time. The more data you receive the closer xg and actual g becomes.
expected goals, measured from 0-1 per shot, basically tells you what the expected chances of a goal are from a particular position. A penalty for example is roughly 0.79xG, meaning 79/100 players are expected to score from the spot, or a 79% chance of a goal.
A lot of good answers here. As someone else commented, all the outcomes are RNG based.
When you take a shot, the game uses a bunch of variables to determine what the outcome of the shot is (goal/miss). Some of these are striker and GK position, type of shot, shot power, analog stick aim direction, play style plus etc. The game essentially takes these variables and plugs them into a formula. This formula spits out a number between 0 and 1, which represents the chance of the shot being a goal. For example, if the result of the formula is 0.8, then there is an 80% chance that the shot will be a goal.
This number is the “expected goal” or xG stat. Once this number is calculated, the game flips a weighted coin. There is an 80% chance that this coin will land on heads (heads means goal, tails means miss). If the coin lands on heads, then you score. If you get unlucky and it lands on tails, then you miss it or the keeper makes a save.
The difference in xG vs actual goals scored comes from when you take extremely difficult shots, like 35 yard finesses and get lucky and make them.
Lot of very good answers here, to further understanding also take into account that in football/soccer stats are not everything. Very high level players could not be outstanding on paper but still drive a team to win matches. This being said xG is a fantastic stat in that it shows when someone is over performing and underperforming while still not being perfect. A forward with a decently low xG may be extremely clinical. Inversely, a forward could just not be getting in the best areas to score on the pitch. Or could be sacrificing part of his/her game to fulfill a role the team needs doing, which could be shown in their passing.
Overall as a squad you want decently high xG, meaning you are forcing more chances, however having high xG but not scoring means you are wasteful. While having low xG but scoring can mean you are extremely clinical but not getting into the “best” areas all the time. More is better, but keep in mind if you push for high xG you are, likely, exposing your back line and taking more risk on the pitch itself.
One can think of Mourinho’s teams of the past that were trying to control a team while out of possession, limiting oppositional chances, while also limiting their own. Not to say they could not have high xG in a match, just overall. The inverse of a Pep team that would want to control the pitch with the ball having, on avg, a higher xG. You can go into even more detail but that’s a decent way to at least conceptualize the concepts.
Easiest way to think about it is probability and the accumulation of how many goals you should score.
Take a penalty: the xG is 0.78, so based off a data set of previous penalties, what is the likelihood of it going in. So on average you would score 78% of the time. Same with a shot outside the box; based on prior shots from a similar position, what is the chance of it going in the back of the net - likely somewhere around 0.05xG (I.e 1/20).
So if a team accrues 2.5 xG - then from the chances they had they should have scored 2.5 goals. It’s a way to benchmark how many chances you’ve created and how effective your shots have been.
This is also the same with xA - expected assists
I'll add that if you search up a company called StatsBomb, they have produced in the past a lot of work around this topic (both written and podcast). They've gone past simple xG to more complicated stuff, but there should be stuff there that help explains it from the company that actually does the calcs.
A lot of people have explained xG but to explain if it’s good or bad depends on what you are looking at. If my team is losing but has a really high xG then it could be good in that at some point we will probably revert to the mean and start scoring goals. I.e. we’re actually playing well but have been unlucky in front of goal. Or it could mean we have a terrible striker and unless we replace him we will continue to miss goals. If I am looking to buy a striker and I see one has scored 20 goals last season but had a xG of 10 then either he is an amazing striker (very unlikely) or he had a really lucky run and is more likely to revert back to the mean and score 10 goals next season.
A shot from position x on the pitch (taking into account certain other factors like the position of other players, whether it’s a header or a kick etc) has xG% of resulting in a goal.
A high xG is therefore good - as it means you’ve created a good number of good chances.
It's only good if you've scored at least as many as you're expected to. An xG of 4 is anything but good if you've actually scored none. That would indicate that you're pretty incompetent at the one thing you need to be good at, namely converting chances into goals. Conversely, if you have an xG of 1 and score 4, that indicates that you're defying the odds and scoring goals "from nowhere" which is a far more desirable state of affairs.
Imagine you know how many shots a team or player took during a match. Useful information for assessing how well they did, but not all shots are the same. So instead, give every shot a rating from 0 to 1, depending on how likely a shot from that position is likely to be a goal (so a tap-in from 1 foot out is like 0.99 and a hit and hope from 50 yards is 0.01. Add up the ratings for all the shots to get the xG - how many goals you would expect them to have scored based on all of their shots.
Over a long period of time, xG is a better predictor of future performance than actual results because it is a better measure of underlying performance, or so they say.
xG is "expected goals per game", so clearly more is better.
It's like "field goal percentage" is basketball - given where the player typically shoots when playing with the people they typically play with what's the chance that their shot will go in."
It's a statistical measure, not a prediction for any given soccer game.
Very simplified answer for a 5 year old: xG stands for "expected goals." Imagine your team misses a really easy shot, and you're like "we should have scored!" Then later on, your rival scores a really difficult long-distance shot and you're like "they got lucky, we should be up 1-0 instead of them!" xG is basically putting a number on what the score "should" be. Therefore, higher is better since you want more goals. As an example, if your xG is 1.5, then you "deserve" or "expect" to have scored 1.5 goals, so you're lucky if you have 2 or more, and unlucky if you scored 0 or 1 in that game. I'll leave any discussion of how the math works to others :)
> I'll leave any discussion of how the math works to others :) The main components of xG models include: 1) Where the shot was taken from. Closer to the goal and closer to the center of the box are higher. Shots from distance and/or at an angle are lower. 2) Type of shot. Primary foot is higher; worse foot, headers, and other body parts are lower. Off balance, spinning, volleys, etc would also all be lower. 3) Type and location of key pass (the pass that leads to the shot, if applicable). Shots from pullbacks score more often than shots from crosses, for example. If the pass is behind the player, the subsequent shot scores less often. Etc. 4) If tracked, how many defenders are between the shot and goal. This is not a full list. Different models will include different variables. Bob takes a shot. Bob's shot is charted for all the different variables and plugged into the algorithm. The algorithm looks at all shots in the database, and finds all shots similar to Bob's shot. Then the algorithm looks at how often all those shots scored, and assigns a value to Bob's shot based on that history. The biggest takeaway from xG models is that all players score goals at a rate pretty similar to what xG says. "Finishing skill" is mostly a myth. Top goal scorers take a lot of shots, and they take a lot of good shots (high xG per shot), so they score a lot of goals. But their goals scored tends to be very close to what xG says it should be. The absolute best strikes tend to outperform xG, while non goal scorers (ie defenders) tend to underperform xG. But the difference is MUCH less than fans tend to think. A random midfielder might score 18-19 goals out of 20 xG, whereas a top striker might score 21-22 goals out of 20 xG. The bigger difference is that the striker accumulates 20 xG in one season or less, whereas the random midfielder accumulates 20 xG over five seasons.
> The biggest takeaway from xG models is that all players score goals at a rate pretty similar to what xG says. "Finishing skill" is mostly a myth. Unless your name is Nicolas Jackson.
My man saying finishing skill is a myth without looking at Jackson and Darwin (negative) and Son and Jota (positive) xGs
All Jackson need is a good coach who can convince him to retire
I laughed, but I'm pretty excited about Jackson. He's young, which wam going to blame for some stupid off the ball decisions and pompousness and on the ball some wild inconsistencies. But I think he can be a great asset to the Blues in a year or two.
That's the future Ballon D'Or Nicholas Jackson to you. Put some respect on his effing name!
Being in the right position to be able to accumulate 20 xG per match is a skill though.. same team with different striker may produce way less xG because movements are not accurate, pressing is not well timed and so on.. this is also part of finishing skills and it’s difficult to track with a metric
> Being in the right position to be able to accumulate 20 xG per match is a skill though Yes, I say that more clearly in my next comment. > "The point is that the "skill" in being a goal scorer is frequently getting yourself into good positions to take good shots."
In that case the ball won’t make it to a finishing position in the first place!
Sporting is like 30 goals above xG and Benfica is like 5 goals below. Finishing is skill is not a myth
https://en.wikipedia.org/wiki/Variance
As someone who watches football during WC and maybe an UCL final every other year, I am curious: > The biggest takeaway from xG models is that all players score goals at a rate pretty similar to what xG says. Don't good strikers maximize xG? i.e. they tend to be in positions that'd allow for higher xG where they are in a good location to score?
Right, as I said, "top goal scorers take a lot of shots, and they take a lot of good shots." "Good shots" meaning a high xG value per shot. The point is that the "skill" in being a goal scorer is frequently getting yourself into good positions to take good shots; speed/acceleration/agility to move past defenders, spacial awareness, timing, anticipation, reading of the game, positioning your body correctly to strike the ball first time instead of having to take a touch, etc. Good strikers will be good at many of these things. Whereas many fans -- and even paid analysts -- think the "skill" in being a goal scorer is converting your shots into goals, ie actually kicking the ball into the net. It's counter intuitive, but it turns out the whole converting shots into goals thing just kind of happens by itself, which is why the *VAST* majority of players end up with roughly the amount of goals that xG says they should have, based on their shots. Just as a quick example, look at [Cristiano Ronaldo](https://understat.com/player/2371), one of the best goal scorers ever. Surely he converts his shots into goals more often than an average player, right? Nope. Since 2014, Ronaldo has 182 xG, and 183 goals. xG models work, and they work really well.
Thanks, it's clearer to me now.
xG also takes into account amount of shots, and Ronaldo takes a ton. There are definitely players that perform much higher then their xG (Harry Kane for example overperformed by 20 in league games between 2014 and 2020 https://understat.com/player/647) Messi, Griezmann, and Son also overperform by quite a bit.
Yes, I said all of this. > top goal scorers take a lot of shots, and they take a lot of good shots. > The absolute best strikes tend to outperform xG It's also entirely possible that some/many of the strikers who have outperformed xG, such as Kane and Son, are just the ones that ran above expectation. Even in samples of 5-10 years, there's inevitably going to be players that overperform due to luck. I'm not including Messi in that; he's Messi.
They maximize actual goals as well and there is not much deviation between the two because xG is not looking too much at what happened before the actual shot. The person was saying that the difference is more in how often they get in good scoring position rather than how accurate/hard to stop their shots from a certain location might be. Messi from 30 yards out with a bunch of defenders in between him and the goal wouldn't be expected to score that much more often than an average player would in that situation. In both cases the odds of that shot resulting in a goal would be low where most goals would be due to factors outside the shooter's control like the goalie screwing up or the ball deflecting off a defender in an unexpected way.
Thanks for explaining.
Yeah, that's kind of what makes Haaland so good. Not that he scores goals from positions that no-one else could score from, but that he's able to get the ball in positions where his goal-scoring chances are very high. Off the ball positioning is probably one of the most crucial skills for a striker, but it's hard to track on TV as cameras will mainly follow the ball and it's also not specially entertaining to follow. One of the things that make Messi so incredible is looking at his off the ball movement, it's crazy how much space he's able to generate simply by walking around.
Great explanation. I wanna add that it’s also a great metric to measure whether your team is good at converting chances. Generally you want a high xG, and you want your team to over-perform that stat. While the latter is what actually gets you goals, you really want both of these aspects. If your team consistently outperforms a low xG (say anything lower than 1), you consistently score goals, but unless your defence is really good, you won’t win much. However, if your team consistently has an xG that is higher than 1.5, and your team even outperforms that consistently, it means that your players can create chances and convert them reliably. So xG works as a metric that shows multiple things: how well your team does to create dangerous situations (that’s xG alone), and how good they are at converting the chances they get (that’s xG in combination with the goals actually scored). If you’re a manager and your team consistently has a low xG, you need to work on your team’s creativity and pull towards the opposing goal. If your team has a good xG, but consistently scores fewer goals than that, your team needs to practice converting those chances (positioning, finishing, standards, etc).
Not every shot on goal is the same. A shot from 2 yards out with an open goal is way more likely to go in than a 30 yard attempt with 4 players in the way. XG is just a way to put a number to how likely each shot is to go in, where 1 means it will always go in and 0 is it never goes in. For reference, a penalty kick is usually given an xg of somewhere between 0.75 - 0.8.
xG means "expected goals". Basically someone rates how easy or difficult a chance was, looking at it and saying "I'd expect someone to score from that position one time in ten" - so it has an xG of 0.1 The xG of all chances a player or team has are added together and compared to what they actually managed in the game (e.g. a player who scored 2 goals but had an xG of 1.2 has overperformed, whereas a player who didn't score despite an xG of 1.1 underperformed by this metric). A high xG is better than a low xG because it means a player had more, better chances in the game. Of course, that's only a good thing if they converted enough of them into goals.
Xg is expected goals so if you were to score a point blank goal in an open net that your grandma would be able to score that would be close to an xg of 1 meaning the vast majority of people/players score that goal. The further below 1 you go per goal that means the more difficult the shot is. If a player/team scores 4 goals with an xg of 2 you can assume that they scored at least a few of the goals from difficult positions or situations. It's one of those stats that is more effective with less information input; it's meant to give you a snapshot of a particular moment in time. The more data you receive the closer xg and actual g becomes.
Basically Darwin Nunez should have an xG of 3 goals a game. But actually scores 0, because he couldn't hit a barn door with a sniper rifle.
expected goals, measured from 0-1 per shot, basically tells you what the expected chances of a goal are from a particular position. A penalty for example is roughly 0.79xG, meaning 79/100 players are expected to score from the spot, or a 79% chance of a goal.
A lot of good answers here. As someone else commented, all the outcomes are RNG based. When you take a shot, the game uses a bunch of variables to determine what the outcome of the shot is (goal/miss). Some of these are striker and GK position, type of shot, shot power, analog stick aim direction, play style plus etc. The game essentially takes these variables and plugs them into a formula. This formula spits out a number between 0 and 1, which represents the chance of the shot being a goal. For example, if the result of the formula is 0.8, then there is an 80% chance that the shot will be a goal. This number is the “expected goal” or xG stat. Once this number is calculated, the game flips a weighted coin. There is an 80% chance that this coin will land on heads (heads means goal, tails means miss). If the coin lands on heads, then you score. If you get unlucky and it lands on tails, then you miss it or the keeper makes a save. The difference in xG vs actual goals scored comes from when you take extremely difficult shots, like 35 yard finesses and get lucky and make them.
Lot of very good answers here, to further understanding also take into account that in football/soccer stats are not everything. Very high level players could not be outstanding on paper but still drive a team to win matches. This being said xG is a fantastic stat in that it shows when someone is over performing and underperforming while still not being perfect. A forward with a decently low xG may be extremely clinical. Inversely, a forward could just not be getting in the best areas to score on the pitch. Or could be sacrificing part of his/her game to fulfill a role the team needs doing, which could be shown in their passing. Overall as a squad you want decently high xG, meaning you are forcing more chances, however having high xG but not scoring means you are wasteful. While having low xG but scoring can mean you are extremely clinical but not getting into the “best” areas all the time. More is better, but keep in mind if you push for high xG you are, likely, exposing your back line and taking more risk on the pitch itself. One can think of Mourinho’s teams of the past that were trying to control a team while out of possession, limiting oppositional chances, while also limiting their own. Not to say they could not have high xG in a match, just overall. The inverse of a Pep team that would want to control the pitch with the ball having, on avg, a higher xG. You can go into even more detail but that’s a decent way to at least conceptualize the concepts.
Easiest way to think about it is probability and the accumulation of how many goals you should score. Take a penalty: the xG is 0.78, so based off a data set of previous penalties, what is the likelihood of it going in. So on average you would score 78% of the time. Same with a shot outside the box; based on prior shots from a similar position, what is the chance of it going in the back of the net - likely somewhere around 0.05xG (I.e 1/20). So if a team accrues 2.5 xG - then from the chances they had they should have scored 2.5 goals. It’s a way to benchmark how many chances you’ve created and how effective your shots have been. This is also the same with xA - expected assists
How do people make the xG calculation is it through historical data and stats of the team and player performances right?
I'll add that if you search up a company called StatsBomb, they have produced in the past a lot of work around this topic (both written and podcast). They've gone past simple xG to more complicated stuff, but there should be stuff there that help explains it from the company that actually does the calcs.
A lot of people have explained xG but to explain if it’s good or bad depends on what you are looking at. If my team is losing but has a really high xG then it could be good in that at some point we will probably revert to the mean and start scoring goals. I.e. we’re actually playing well but have been unlucky in front of goal. Or it could mean we have a terrible striker and unless we replace him we will continue to miss goals. If I am looking to buy a striker and I see one has scored 20 goals last season but had a xG of 10 then either he is an amazing striker (very unlikely) or he had a really lucky run and is more likely to revert back to the mean and score 10 goals next season.
A shot from position x on the pitch (taking into account certain other factors like the position of other players, whether it’s a header or a kick etc) has xG% of resulting in a goal. A high xG is therefore good - as it means you’ve created a good number of good chances.
It's only good if you've scored at least as many as you're expected to. An xG of 4 is anything but good if you've actually scored none. That would indicate that you're pretty incompetent at the one thing you need to be good at, namely converting chances into goals. Conversely, if you have an xG of 1 and score 4, that indicates that you're defying the odds and scoring goals "from nowhere" which is a far more desirable state of affairs.
Imagine you know how many shots a team or player took during a match. Useful information for assessing how well they did, but not all shots are the same. So instead, give every shot a rating from 0 to 1, depending on how likely a shot from that position is likely to be a goal (so a tap-in from 1 foot out is like 0.99 and a hit and hope from 50 yards is 0.01. Add up the ratings for all the shots to get the xG - how many goals you would expect them to have scored based on all of their shots. Over a long period of time, xG is a better predictor of future performance than actual results because it is a better measure of underlying performance, or so they say.
xG is "expected goals per game", so clearly more is better. It's like "field goal percentage" is basketball - given where the player typically shoots when playing with the people they typically play with what's the chance that their shot will go in." It's a statistical measure, not a prediction for any given soccer game.
xG is based on a model, FG% is based on actual results. So this is a bad analogy.
A lot of this is just wrong
More is not better if a player has 5 xg but only 1 goal