It all comes down the the screams for help. If it was Trayvon, I am baffled as to how Zimmerman isn't facing a murder 1 charge. If it was Zimmerman, why is he facing any charge at all?
Zimmerman needed to be in danger of immediate death or great harm to be justified to shoot a person. He could just point gun and say don't move.
If somebody tries to take my gun, I just shoot. I will not be shot with my own gun.
You don't hold it up and let him wrestle you for it.
Now, this is assuming the claim of Trayvon trying to take his weapon is true.