As a person who has not been trying to follow the case.
1) We have zimmerman's testimony and a police call stating he was stalking martin
2) We have Zimmerman's testimony that Martin started the fight.
a) Assuming Zimmerman's testimony is the truth. Zimmerman was stalking Martin in the rain. When a stranger is stalking you in the rain, you are going to fight or flee. If a fight breaks out that doesn't mean you should get shot, ironically Martin stood his ground if Zimmerman is telling the the truth of who started the fight.
b) If Zimmerman is lying and he started the fight, he stalked and shot an unarmed man.
In neither situation did Zimmerman perform self defense for his actions caused the conflict to start, and they were a logical conclusion of his actions.