You and I must have gotten our news from different sources. I saw nothing that would indicate that Zimmerman had done anything that could have aggravated Martin to the point where he could legally attack Zimmerman. Not only is following someone not a crime but at a distance it should not be threatening. If martin was concerned a simple 'Stop, why are you following me?' or 'May I help you?' would, I expect, cause Zimmerman to identify himself as Neighborhood Watch. If the reports are right that Zimmerman was attacked after turning to return to his car it would indicate that Zimmerman was not following close enough to keep track of Martin.
Martin may not have done anything illegal, before possibly attacking Zimmerman, but it was Zimmerman's job to identify things that were out of place. Certainly someone new to the neighborhood would seem out of place. The word pursuit indicates, to me, an intention to catch someone or something. I have heard no claim that Zimmerman intended to do anything but maintain surveillance till the police arrived.
If Zimmerman started this when he started following Martin then no rent-a-cop at the mall could follow a suspected shoplifter. If they did could the suspect then legally beat their head into the concrete?
If you go for your gun every time someone follows you in the mall, across a parking lot, or down the street I expect you must have your hand on your gun most of the time.
There are a lot of if's in this post because there are a lot of if's in this case. So let me drop one more. If you try to beat my head into the concrete I will draw my gun.
U.S. jurisprudence is based on the premise that A: You are innocent till proven guilty, and B: It is better that 100 guilty go free rather than one innocent go to jail. I still have reasonable doubt and I do not have all the evidence.