No disputing that, the question now is, why didn't Martin break off contact and retreat? He didn't and he was subsequently viewed by the witness (according to his documented statement) as being on top of Zimmerman beating on him and attempting to slam his head onto the cement pavement........
Since Martin chose not to break off contact and retreat, he became the aggressor and an immediate threat to Mr. Zimmerman's life...........
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Oh, I don't know...maybe he saw Zimmerman's gun and didn't feel safe to disengage. Maybe the gun was already in Zimmerman's hand. Do you know where the gun was or when/if Martin first saw it?
And, as long as you asked me to speculate...
Maybe he did disengage and was backing off when zimmerman pulled the gun and shot.
The point is that nobody saw the moment that Zimmerman pulled the trigger (at least none of the released statements indicate a witness to that moment). The "big news" of the day was the witness John. But he didn't see the start of the fight, didn't say he saw the gun and was no longer watching the action when the gun was fired.
How far away was Martin from the muzzle? Is there forensic evidence that says two inches or ten inches or two feet or five feet? I haven't seen any.