There has to be more to the story than what George Zimmerman has said. Zimmerman is a very big guy and would appear more so on a rainy night. It seems like any normal kid would just be relieved to get away from this large stranger rather than approach him and try to take him down.
Trayvon referred to Zimmerman in his phone conversation as "creepy," which insinuates he was a little scared himself. It seems like the most a scared kid could hope for would be to get a punch in and then run for it. For things to have happened the way Zimmerman said, it seems like there would have had to be some mincing of words to fire Martin up enough to tackle this guy, straddle him and try to smash his head in. With these two being strangers, it probably would have had to be something racist to fuel enough fire in Trayvon to do what he did.
Zimmerman's history seems to prove he is not racist, but in the heat of the moment people often say what they think will inflict the most damage, even if they don't mean it.