yes, but only because an unarmed guy isn't a threat to anyone in a car.
let me give you a possible explanation for what happened.
zimmerman sees the unknown kid, suspects hes a buglar casing houses
he follows him
kid cuts through someone's lawn to try to get away
zimmerman catches up, and corners him
asks him what he is doing in the neighborhood.
kid gets angry/scared, lashes out, gives zimmerman a bloody nose and start pounding his head into the pavement
zimmerman calls for help. no response.
zimmerman, afraid of grave injury, shoots the kid. one bullet. kid dies.
now this isn't necessarily the way it happened, but its plausible and fits all the facts. Even without the stand-your-ground law, this could possibly be excused under Excusable Homicide. With the law and certain cases for precedent, I don't see how zimmerman isn't found not guilty. The precedent I keep bringing up is from cases involving drug dealers that were defending themselves from attack from other drug dealers who accidentally hit & killed bystanders but were found innocent because of the stand-your-ground law.
this is why the grass stains and wounds on the back of zimmerman's head are so absolutely crucial. Because the only way I can see that happening is from Trayvon kneeling down over zimmerman and beating him. As long as that is true, there wasn't anyway for zimmerman to defuse the situation or leave the scene once the hitting starting. That makes it excusable homicide.
so basically if you kill someone make sure there's some minor trauma anywhere and you'll be good to go