Where did you read this? That sounds dumb to not ward off blows.
He didn't have to ward off blows, here is Zimmerman arriving at the police station that night:
http://abcnews.go.com/US/video/george-zimmerman-police-surveillance-16024475
That look like someone who was pinned down getting hit in the head? How about someone with a broken nose?
The mods delete any new threads on this, so I'm trolling all the threads with this stuff, which is HUGE.