I have to ask; what evidence have you seen that suggests this is appropriate? To me, the 2 most solid bits of evidence to the contrary are:
1) Police dispatcher telling him (about following Martin) "We don't need you to do that" and Zimmerman responding "Ok", then stating he lost the guy. 2) an eyewitness stating he was physically present and witnessed Zimmerman being held down and beaten and Zimmerman yelling for help to which the witness replied he was going to go call e911.
We haven't seen the medical reports or a lot of other things just yet so I'm unwilling to make any assumptions about what we will see. Everything else is speculation... even the part about Zimmerman claiming Martin was trying to get hold of his gun and threatening to kill him... all unsubstantiated.
There were two (2) witnesses that saw Zimmerman on the bottom and calling for help...one was John (interviewed on local TV), the other was Austin Brown, the 13 year old black boy, who was interviewed by ABC (not sure if local or national).