I don't mean to trivialize this, I hope the guy is ok and I don't know at all what happened to start this fight, but it appears that a Celtics fan showed up to the Lakers stadium in a Celtics jersey and got a whole lot of punches throw his way.
BOSTON (WBZ) ― Tempers got out of control at the Staples Center in Los Angeles Sunday night while several Laker fans watched a televised broadcast of Game 2 of the NBA Finals in Boston.
In a video posted on YouTube Monday, a fan wearing a Celtics jersey found himself in the middle of a group of angry fans and punches were thrown.
No one has been identified.
You can see the widely circulated youtube here. But the following one was posted in the forums and shows some of the events a little more clearly. In fact, you can watch as one Laker fan picks up a chair and throws it at a Boston fan. Classy.
With that said, I can't imagine any reason to go to a viewing of the game in the Lakers stadium. It isn't like attending a live game where you get to see it played in front of you. You are just watching TV ...with thousands of Laker fans. If this guy was looking for trouble, he sure picked the right place to find it, and he sure found it.
(Update: as pointed out in comments, these may be 2 different incidents)