It's this simple - George Zimmerman was stalking Trayvon Martin

[slackmaster]

9. The defense will admit that Zimmerman was following Travon, but lost sight of him and broke off...

..the pursuit. Some time later (even if that is only seconds or tens of seconds) Trayvon came out of the shadows and attacked Zimmerman while he was walking toward his vehicle. So the story will be that the "stalking" (and they will not allow it to be characterized that way if they can prevent it) had ended and Zimmerman no longer posed a threat. That is clear from the staged re-enactment video.

Zimmerman at any time could have gotten into his vehicle and driven away.

The defense is going to claim that Zimmerman was in the process of doing just that, or that he planned to sit in his vehicle and wait for the PD.

Zimmerman's version has plenty of inconsistency that will be exploited by the prosecution. They may be able to pull off a conviction on manslaughter, but convincing the jury of malice aforethought (required for a murder conviction) will be very difficult even if Zimmerman's claim that he was attacked without provocation during a second encounter falls apart.