Of course not... IF that's what happened. But there is the bit about how he pursued the young man against the authorities request. All things that will be weighed by a jury. An affirmative defense (in this case, self-defense) requires Mr. Zimmerman to prove that narrative.
You're probably right, but is that necessarily a good thing?
Personally, I've only seen evidence that he pursued a young man who he "Thought was up to no good;" no evidence that the boy even was in fact "Up to no good..." He was probably emboldened by the fact that he had a gun, a fight ensued, and he shot the boy when he began to lose.
IF he started the fight (which you might argue he did just by virtue of his pursuit!), I don't even think the narrative you've provided constitutes self-defense. Trayvon may well have went for the gun out of fear of his own well being in that scenario.
Personally I think he'll be found guilty. But nobody to my knowledge who thinks he's guilty wants to forego a trial, and yes, it irks me when the very Zimmerman supporters who seem to want to skip the trial and move directly to exoneration accuse others of the very offense that THEY THEMSELVES are guilty of.