When I was a school boy the boys had very strong ethics about fighting, including:
No weapons
No hitting below the belt
No hitting a man when he was down
No kicking
No surprise attacks
No picking on those smaller than yourself
No attacks on those who wore glasses or who were disabled
Peer pressure insured these rules were followed.
Fights detected by teachers were automatically and immediately punished by four strokes of the cane regardless of who started the fight. Fights always attracted a crowd which ensured likely detection by prefects or teachers who usually approached quite undetected.
There were few fights and none causing serious injury that I am aware of.