Except he wouldn't have broken the law if he believed he was protecting himself. The beauty of the Florida stand your ground law is that it's so broad that had Martin killed Zimmerman he could have plead self defense. Except for the fact that he was black and not the son of a judge.
Florida's stand your ground law protects the instigator. That's the point of stand your ground laws. Prior to SYG the standard was that you had to try and avoid or escape situations that require deadly force. Florida's statue is so broad that believing you are preventing a felony is a good enough reason to shoot to kill.