Well, this close up video of the situation when CM Punk ran up into the stands at Monday Night Raw in Sacramento, California, shows exactly why CM Punk reacted the way he did.
He was pushed twice and the fan he punched hit Punk in the back of the head just before Punk turned and swung on him. But was the fan intending to hit him?
Judge for yourself:
That seems like it's clear Punk is simply retaliating to getting hit multiple times.
But does that make it okay?
UPDATE: After a closer viewing with my Cageside colleague June M. Williams, it seems obvious the fan in the sunglasses did hit Punk but he was not intending to do so and instead was actually pushed into Punk by a man standing behind him.
If you look closely (and I'm sure you have), a man actually pushes his way up to Punk's back, directly behind the man with the sunglasses, and shoves Punk before flipping him off and then smacking him in the back of the head. Punk, mistakenly thinking it was the man in the sunglasses, retaliates on the wrong man.
To be clear, the title of this post is not meant to imply that the man in the sunglasses hit Punk, just that Punk was shoved twice and hit in the head before punching the fan. That is all. Sorry for any confusion.