I was tried once to see if I was someone fit to bully.
I'm very skinny and one of the smallest girls in my year and so was seen as an easy target by the 'tough' girls.
Three cornered me, began punching me, two held me down to let the leader take shots at my head. I got out of their grip, punched the leader, jumped up to kick them in the head and they ran like cowards and were too afraid to bully in the school again after that.
I also called the cops on them and they got permanent criminal records because of it. Because it was completely unprovoked and a lot of people knew that. All 4 of us were 16 at the time.
The way to stop bullies? To give them a taste of their own treatment. They don't like it. It scares them senseless when they find someone who isn't afraid of them.
Well, that's in my experience anyway...