That is the $64,000 question. Nobody seemed to witness that part of the confrontation.
What is know that it was Zimmerman who did the initial chasing of Martin.
Bigger question is if Zimmerman already had his gun in his hand when he confronted Martin.
There is the old adage, that has merit to it, is that you charge a gun and run from a knife.
But once again this all comes back to the police dept who handled this like it was a jaywalking case.