His story was the confrontation did not happen until after he had lost contact and he was going back to his car. There is no evidence from the police reports or any witnesses that he accosted Martin. It appears that Martin didn't like being followed and followed Zimmerman back to his vehicle and punched him. If that is the case, then Martin was guilty of assault and Zimmerman had every right to defend himself.

Maybe Zimmerman shouldn't have followed, but it doesn't appear that he got out of the vehicle intent on a confrontation, that is strictly your interpetation.