Kids fighting

[jdm4x43732]

My wife and I are raising our niece and nephew along with our two girls. Neither of their dads are in the picture and mon is useless. He has had a rough life and has been picked on in school. He has beat up 3 kids lately. All kids who either bullied or hit him first. I'm proud of him for taking up for himself but we had to pick him up at school last week cause he put a shiner on some kid for picking on him for not wanting to fight in the locker room. Anyone got ideas on how to make him understand how quickly this can turn bad. I sure don't need to pay some kids medical bills or go get him out of jail. He is about to turn 13. Punishment, boxing or karate for discipline? Whip him? Anyone else with teenage boys and this problem?