Yep, this is stupid to fight over sports teams.
This happens sometimes. Alcohol and drunken behavior could be part of it.
Why is there such emotion over sports teams? Somebody talks trash about your team, or says they hate the guy whose jersey you are wearing, so you think you should respond with violence? Somebody threw the first punch, and I wonder what the provocation was.
Alcohol induced loss of normal inhibition of fear and violence response to perceived threat. Or in the vernacular...a buncha dumb drunks.