@maxdancona,
As a writer you make a pretty good physicist. That's a terrible sentence, people don't stop punching someone because they get bored.
There are plenty of other reasons why they'd stop, the opponent is sufficiently injured/immobilised, their anger subsides, they use up all their energy, they have second thoughts or someone stops them. Boredom doesn't come into it.
Sentences need to be believable and yours isn't remotely so.