First, he'd been trying to start a fight with me for weeks.
He squeezed me around the ribs without one of my arms in between, trying to crush my ribs. In high school you must have an arm trapped when you squeeze like this (or at least, that's how it used to be). I was on all fours--he got to start on top. The reason was that I was on the wrestling team and he wasn't, plus I was 5 pounds heavier than he was. (Yes, this genius decided to wrestle a wrestler who outweighed him. He insisted on it--I had declined to wrestle with him because I knew he was looking to cause trouble, but the gym teacher said I had to accept the challenge of a match.) I sat out, broke his grip, then as he stood from his kneeling position I did a hip-throw, slamming him on his back. Yes, my knee touched first, making it legal. With all the air knocked out of him I slipped on a headlock that was actually a choke--but this gym teacher was the basketball coach and only knew that it wasn't illegal because I had an arm in there. A wrestling coach would have recognized it as a choke/potentially dangerous technique and stopped me. It may be that my technique wasn't clearly illegal but it certainly was a technique that could have been disallowed at the referee's discretion. I had his bicep across his throat and was cutting off his air.
I held him down, choking him, carefully keeping one of his shoulders off the mat. The gym teacher looked at me quizzically, as he could see that I clearly could have pinned him but wasn't doing so. As the kid started turning red, he took to swinging an arm at me and actually trying to punch me. When he started turning blue, he began reaching out toward the gym teacher for help. (He couldn't speak.) The basketball coach looked at him, looked at me, and then made a "pin him" motion with his hands. I did.
The kid never hassled me again. There's someting about being choked purple that changes a person's perspective on things!