[Adam]

Assuming I'm on the JV game, if they're screaming obscenities, they're leaving the game. I wouldn't let Jimmy's dad do that, not when it's done in a way that it gets and keeps my attention.

Find a stoppage in play, talk to the AD, and let him/her know the coach needs to knock it off or leave.

Also file a report with your assigner AND directly with the state governing body.

If I'm part of the crew for the varsity crew and I'm watching this game, I'd ask the crew at half time why they aren't dealing with it and let the conversation flow from there. Coach gets zero tolerance from me.