This video was from a full four hours after the shooting, Zimmerman had already been attended to by EMTs at the scene. Any blood on his face or head would have been cleaned up during treatment. His Red Jacket would also prevent any blood stains from being visible. Basically this video proves nothing for either side of the case given the time elapsed and the poor quality.

However: The “Receiving” officer who makes a token display of searching Zimmerman (SOP) does at 0:50-54 seem to be looking at the back of his head in response to a comment made by the escort officer, and then at 1:04-1:07 you see the back of his head as clearly as possible given the quality of the video and there does appear to be a “discoloration,” “spot,” whatever you want to call it in the center top of the rear of his head.

Given the other witness that has come forward claiming to see Zimmerman on his back with Trayvon on top. Trying to claim that no physical altercation took place and that Zimmerman simply executed Trayvon seems like a non-starter/losing strategy. The point that needs to be made is that Zimmerman forced and quite probably initiated the altercation with a kid who was simply trying to walk home from the store.