Have you actually ever been to a BYU game at RES? I've seen dozens of instances of bad yewt fan behavior. I've seen several yewt fans get ejected. They aren't drunk and rowdy just at BYU games, they treat all visitors poorly.
That sort of thing is very rare at BYU. I once saw three guys go to the railing to harass the BYU cheerleaders. One of them threw a cup full of ice and hit a cheerleader. Turned out the three of them were USU fans. They got turned in and ejected from the stadium. Most of the ejections from LES have been fans of visiting teams, not BYU fans.