So were you there, or just expressing opinions?
So that's my opinion after reviewing the video and after-action reports of student-relatives. I think that area (maingate square) is a magnet for crowds, too many bars and too difficult to exit effectively. The sudden exodus at the end of the game caused a flash crowd. At least one of the taverns had extra security herding people back inside off the street after the police started to move. A number of people were effectively blocked from leaving and expressed themselves with tweets..
BTW we got this tweet right at the start of the overtime during the game:
UAlert Avoid Main Gate Tucson Police declare unlawful assembly @ maingate sq. public advised to avoid/exit area