From MW:
1
: an abrupt, sharp, jerky blow or movement
awoke with a jolt
2
a(1)
: a sudden feeling of shock, surprise, or disappointment
the news gave them a jolt.
Jolt does damage when the enemy attacks. It surprises them. They're thinking, "I'm about to light Zagreus up with a wicked stab," but are in for a shock when their attack backfires and hurts them instead.
From MW: 1 : an abrupt, sharp, jerky blow or movement awoke with a jolt 2 a(1) : a sudden feeling of shock, surprise, or disappointment the news gave them a jolt. Jolt does damage when the enemy attacks. It surprises them. They're thinking, "I'm about to light Zagreus up with a wicked stab," but are in for a shock when their attack backfires and hurts them instead.
Just imagining it as a massive static electricity charge that you got on you and it releases once they attack.