I think a school would have a hard time expelling an entire sports team, and a prosecutor wouldn’t want that publicity. A single student? Sure. 30-100 students? Not so much.
When I was in HS, one of the football coaches tried to pull some cr@p he shouldn't have, and benched a couple of starters who wouldn't comply. At the next game, the entire team just sat down and refused to take the field. Much discord on the sidelines, but the coach in question was over-ruled by the other coaches and the team - the WHOLE team - ended up playing the game. No violence, but they showed they were an actual TEAM, not just a bunch of boys. (To be fair, as our team was one of the league's doormats, no athletic scholarships were in jeopardy.)
As for
prosecutions - I don't see an actual, statutory crime if a bunch of girls walked off the field if a guy walked on to compete against them. ESPECIALLY if this was at an inter mural event and girls from SEVERAL schools walked off.