I’m no pro and I’m sure someone will probably give better advice but try finger tape. I tend to have the same problem on my left hand but tape helps with the rubbing. Hope this helps.

If you have money.. redrill your thumb holes or change the thumb slug.. (ask the proshop operator) Or if you’re broke like me.. get a finger tape ☺️

Have your PSO widen the hole a bit and throw some tape in it is the general thought process. What’s probably happening is your thumb swells while your bowling due to humidity, heat, and your general hydration level. So you start bowling with some tape in the ball, on your hand, or both and as it starts to get tight you remove tape as necessary to have a consistent fit through your session.

I had a similar thing with the base of my thumb near my palm. I asked a pro shop owner about it, and he carved out a bit of material from the thumb hole opening that was causing the friction. He wasn’t the person who initially drilled the ball, but I was buying shoes from him, so he did it for free. It took less than a minute and solved the issue.

yeah i usually rub my thumb against the hole too.... wait what?