My theory is that he pulled the gun out at the moment he decided he was going to follow Trayvon into the darkness behind the condos. With a gun in his hand, he confronted Martin and Martin logically viewed that as a threat and slugged Zimmerman in the face and a fight began. According to eyewitness testimony, Martin was on top AND Zimmerman was on top. I believe that is not conflicting testimony and, because there is a long trail of items belonging to both Zimmerman and Martin, it suggests a struggle was more than the stationary scuffle that Zimmerman said occurred with Zimmerman's head on the sidewalk and his body in the grass.
This paragraph explains why I believe the gun had to already be out (or at least it didn't come out when Zimmerman claims) In my view, there is absolutely no way he could have pulled the weapon out with Travon's knees in his armpits (as he described to his best friend the night of the incident), the gun snugly tucked into a holster inside the right, back hip and covered by a shirt and a jacket. If his story is to be believed, he reached around Travon's legs (instead of blocking some of the 25 blows that were being rained down upon him or cushioning the back of his head with a hand to keep Martin from continuing to bash his head onto the cement), under his body and maneuver his hand under two layers of clothing, over his belt and grab the gun, pull it from the holster and pull it back around the body of a man (who presumably did not try to stop him from doing this, even though he was supposedly in a dominent postition to prevent him from using the gun).
If Zimmerman had his gun out when the confrontation started, he can hardly claim self defense. I know it was more than a couple of sentences, but that is the scenario that I think makes the most sense, given what I know about the case.
