Actually, it does matter how it began. Individuals have the right to defend themselves from assaults and batteries. There does not have to be contact made for there to be an assault or battery (Criminal definitions, not torts). People also aren't 'defenseless' on the ground, although a lot of people do not have good ground defense techniques.
Now, if some guy is following me around, I'm going to try and first avoid it. Martin did that, based on both Zimmerman's call and Martin's girlfriend's call. That's a smart policy. Zimmerman got out of his car and looked for Martin, for whatever reason. (avoiding the speculation). I find that piss poor judgment at best. What we don't know is how Zimmerman or Martin acted between this time and the shooting.
IF (speculation) Zimmerman was closing into close contact range (you can speak from a distance), I'm going to, based on known action, assume that he has bad intentions and not wait for him to throw the first punch, and I'm going to stop the threat by knocking him out (so he can no longer fight) and going home.
If he was returning to his car and was jumped by the deceased, then there is no doubt Mr. Zimmerman was well within his rights to defend himself the way he did. Period.
If no proof can be obtained that Mr. Zimmerman instigated the attack upon himself, he should have nothing to worry about aside from a vindictive government bent upon incarcerating him to appease those squealing for “justice”.
Believe me, I understand what you're saying, but no indications have been presented, at this point, that Mr. Zimmerman actually instigated the attack upon himself.
How about I speculate some like so many have on this board.
Perhaps his girlfriend goaded him into attacking Mr. Zimmerman whilst they were talking on the phone... It certainly wouldn't be any more implausible than the scenarios I've seen from many on this forum already convicting Mr. Zimmerman of Murder or Manslaughter.