They both should have just stopped. The young guy should have just been quite, and the old people should have just left him alone. I can understand them trying to get him to quiet down, but they had no right to attack him.

Let me say this:  If I were responding to that scene, EVERYBODY would have been in trouble.  After the fact though, after a little investigating, the young guy would be completely innocent.  A fight in public is classified as "affray".  It takes two people to fight.  One or both parties should have walked away.  The young guy was clearly defending himself, though. In the heat of the moment, without any information at all, you treat everybody the same.

As for the people within earshot of the entire incident that suddenly gained courage when the odds were 20 to 1--lame.