Here's what today's society has become:
Someone in that situation who "steps up" to try to stop him will be vilified by the other Bama fans cheering him on, labeled as a party-pooper, told to mind his own business and possibly threatened.
Other people his age or younger would be told the above. Anyone older probably would be the "old man butting in ... we're just having a little fun!" and probably at least verbally abused by the gang mentality.
So what happens? Nothing.
Exactly, but the right (and least dangerous) thing to do would have been to quickly walk away and call the police.