I disagree.
Nobody has provided evidence that Zimmerman threw the first punch, or that he even approached Trayvon in such a way that would have justified Trayvon throwing the first punch.
In fact, nobody has proven that Zimmerman approached Trayvon at all.
According to Zimmerman, he was on his way back to his truck when Trayvon approached him.
Do you know of any evidence that shows this isn't the case?
Yeah, I watched a video of him reenacting the entire evening for the police the day after the shooting, before he hired a lawyer. He was stalking the guy. The police told him not to get out of his car and follow, but he did. He says he lost sight of him and was doubling back to wait for the police when they spotted each other on the way back. Martin asked him what his problem was, then attacked him (Zimmerman says it was out of the blue in the video, but I seriously doubt that - he was trying to shine the best possible light on himself.)
I don't know what he said happened after he got a lawyer, but I gather it was different, but not all that different.
Having been chased around by a creepy dude myself, I call that a pretty clear case of provocation, and an "approach". If I had felt strong enough to confront the man who was following me, I probably would have, but I was a 13 year old girl and he was a grown man, so I skedaddled.
According to Zimmerman, when Martin confronted him, he asked "Do you have some kind of problem?" implying that he was very aware Zimmerman had been following him around. If you want to split hairs and not call stalking somebody a form of "approach", then fine, but it's still a pretty clear case of provocation.