Utah had just scored and the cheerleader was waving a Ute flag. (Yes, there was a little taunting going on).
I thought the young fan deserved what he got. He just made a dumb decision by going onto the field. IIRC, he tried to tackle the Ute male cheerleader. The cheerleader was surprisingly strong and not a guy to mess with. (Not a wimp like some might expect)
It was a pretty one sided fight with the cheerleader throwing most of the punches. It was an embarrassing moment for BYU fans as well as the loss.
Oh, one other thing. After the fight was broken up, the Ute flexed his muscles at the predominantly Y crowd. He received a resounding boo for his efforts. Ha ha.