I referee volleyball. Our instructions are to get the home team - preferably the athletic director or somebody similar but ultimately the home coach if there's no one else - to do something about somebody behaving in an unacceptable way.

We're advised not to act too friendly with coaches because some people might think we're favoring their team. Involving the coach if you don't have to might create the opposite impression, that you're upset with the coach or team.

I've never experienced or heard of this being an issue in volleyball. I'm sure it's happened, particularly at the club level where parents are paying big money for their kids to play. Other sports, particularly basketball or football, it definitely happens.