Has anyone succeeded in decoding the "what" and "why" of the fight that broke out in the 2nd Quarter of the SB, immediately after Ed Reed's interception?

I'm re-watching the game right now on YouTube.

Offsetting penalties were called on Corey Graham (24) and the 49ers' OT (74) Joe Staley. But all I could see was Carey Williams trying to beat the crap out of somebody on the ground. (Before he got up and shoved the ref.) Williams was the one who seemed most upset. Any ideas why?