tell me why
Because Zimmerman did not actually instigate a fight. He thought Trayvon may have been doing something wrong so he watched and made sure he was being fine. If someone's following you, you don't have the right to jump on top of them and beat the living stuff out of them. The legally conscious and smart thing to do would be to call the police (he had his cellphone on him) and say "this creepy dude is following me."
But Trayvon decided to beat him stuffless. So what would you do if someone was pounding your head into the ground and you had a gun in your pocket? You'd shoot them. Sorry, it's just what you do when you're getting beaten to a pulp, you take action to protect yourself.
If Zimmerman had shot at the guy or decked him in the face, it wouldn't have been self defense. You can't just pick a fight then shoot someone and claim self defense.
