I was bullied in highschool for a couple of years. I was smart, geeky but had an opinion. There might have been a factor of one guy setting up others against me. It made my life properly miserable. Until one guy pushed the wrong button at the wrong moment. I pushed him off a set of stairs and bashed his head into the radiator. I was stopped pretty quickly by a teacher. There was no serious harm done. My only regret is that I didn’t do it earlier. Up until then I avoided fights. After this incident I was never bullied again.

These days you see a lot of people who say violence is never the solution, bullies are the sad and insecure ones and we should feel sorry for them. We should not. If they are willingly and knowingly making other kids life miserable they deserve nothing.
And if you stood by and think you can clear your conscience by complimenting the one who was bullied? Shame on you too.

So: Violence is an acceptable solution. And bullies don’t deserve pity or forgiveness in any way.

Edit:
Maybe I should make clear I’m not advocating any kind of permanent damage. Scrapes, bruises or a black eye are the extend of it.