I've been to every Utah home game since 1998 except for the two years I was on my mission and never once have I seen a beer thrown at a fan....not one single time. I've never even seen a soda thrown at a fan.
I've seen fights, I've heard swearing, I've seen some drunk off their rocker Ute fans....but I have NEVER seen a fan throw a beer can or soda at another fan.
Fans are nasty at all stadiums to opposing fans....especially rivals. I'll be the first to admit that Utah fans, especially those that consume alcohol before the game are more vulgar to byu fans than byu fans are to utah fans, but that doesn't mean rude things don't come from byu's side as well.