Guy in white shirt and shaved head hits CM Punk in the head
CM Punk turns around and hits a different guy, putting on his sunglasses
This guy's face says it all:
Here's how the whole thing went down
The WWE made a statement about the incident to TMZ:
"WWE security was unfortunately not in the appropriate place at the time. Given CM Punk's persona as a 'bad guy' fans were naturally heckling him, but unfortunately a few fans began shoving him and one struck him in the kidney and on the back. WWE regrets that proper security measures were not in place, and CM Punk apologizes for reacting in the heat of the moment."
Cagedsideseats.com discovered these tweets from the "real" heckler, admitting what he did: