Teacher here. If there's a fight at school, and the kid who's taking a pasting is an arsehole, I don't hurry to break it up. If it's a nice kid, I'll run. And, yes, some kids are arseholes. That's where adult arseholes come from. They don't turn 18 and suddenly transmogrify.
@fesshole I'm sure "taking a pasting" from some bully cannot do anything but improve their character. /s
@EI3JDB when an arsehole kid is "taking a pasting", I'd wager it's more likely the kid being bullied by them finally snapped than another bully.
Speaking from my personal experience of British schools, at least.