A younger girl was being bullied by roughhousing boys over the course of a few days. My son chose the following course of action:
1. Ask some of the bigger kids on his bus how to block punches.
2. Pay close attention as they taught him blocking techniques on the moving bus.
3. Once at camp, hang out with the bullied friend so he would be nearby when someone bothered her.
4. Jump between her and the bullies to block the punches they try to throw at her.
5. After successfully defending her, tell the bullies to stop bulling her.
6. Not bother telling me about this until he brings it up nearly a week after camp has ended. Even then, he only mentioned it when he found out I was scheduling a play date between him and the little girl in question.
I'm particularly proud of the fact that he didn't ask for help learning how to attack, but in how to defend. He wasn't trying to hurt the bullies, just stop the bullying.
That said, he needs some self-defense lessons, preferably in a martial art that emphasizes defense and De-escalation. It's one thing to jump in when the big bully is seven, MAYBE eight, it'll be another matter completely when he's dealing with kids who can knock a tooth out in a fight. Aikido has been mentioned by a few people.