You have to be careful with violence, mfm, though I agree broadly with requiring a willingness to fight in self defence.
If you fight, you need to be mindful of the possibility of escalation. That is to say, there’s a chance that instead of backing down, your bully may instead begin to fight back even harder. The problem with this, of course, is that you don’t know who’s more willing to do however much harm to the other, and if your opponent ends up more capable than you, it could end badly for you.
Well, then at least you’ve got your pride. You could also attack the bully while he isn’t looking if he’s too strong to take on head to head.