A bit of a book is being written here, but w\regards to one-sidedness, I had a similar situation in my senior year in high school (1982).
I beat the hell out of a kid whose mother was a teacher at the rival school I attended each day for vocational classes ( AC-Heating). W\o getting into it too much, he DID ask for it, and it WAS self-defense.
The principal's office was a trip: I soon found out how one-sided things could get.
Not only was I threatened with arrest\failing of the class, BUT I had to sit there with hands proverbially tied as I was verbally abused by the other kid. This kid hid behind the principal's skirts, and used f-bombs, said stuff about my family, whatever, and the principal verbally slapped and shouted me down whenever I defended myself.
Ah, school rivalries...
The kicker??? When I asked the principal if any kid whose mother wasn't a teacher would be allowed to do this, the S.O.B. said "membership has it's privileges."
You have
no idea how
that one made me feel...I knew I couldn't mouth off because this guy meant business, and the added anger of being abused on your rival's native soil w\no way to fight back really made my blood boil..
I graduated a few weeks later anyhow, so they lost and I won
So believe me CC, I know what it feels like to be antagonized and threatened and having the weight of a one-sided wall hit you when you act on your behalf because your back is to the wall.
Good luck, and yes, you did the right thing.