That's what I always find bizarre with stories of bad behavior, why no one takes this simple step. If someone is inebriated, dumping soda/beer, or generally displaying obnoxious behavior...you get the ushers, and that person is warned and then escorted out of the building if the problem persists (or immediately if it's blatantly obvious...like someone pouring their soda on you). It is this way universally at sporting events.

I'd find it pretty hard to believe that the ushers would turn a blind eye, even if it was a BYU fan. There are legal ramifications involved.