Yeah, I witnessed a brawl when I visited my friend in Vegas last month.  
I didn't see the build-up, but I guess the crowd (ie - parents) of Team A were booing a particular kid on Team B.  Team B wins.  That player jumps over to the crowd and talks shit, then everybody starts brawling.
I don't think it helped that the tournament was hosted by a richie-rich school and involved schools from across the tracks.  Maybe it shouldn't matter, but it does.  
Mind you, this was MIDDLE SCHOOL basketball.