I know I'm coming late to the discussion here. And I replied your earlier question, not having seen this one. Since you ask it again though, I'll repost my answer:
Zimmerman wadsn't following Martin at any distance. Martin ran off into the darkness, THEN Zimmerman got out to try to see which way he went, but didn't spot him again until after he hung up with non-emergency several minutes later, when Martin suddenly appeared, strode up to Zimmerman while asking "you got a problem" and then punched him in the nose. That tells me that Martin was watching Zimmerman where he couldn't be seen, listened to the phone conversation, and then, furious that Zimmerman was discussing him with police, attacked. Also, Jeantel said in the Nancy Grace interview that Martin told her that he was in his father's girlfriend's backyard, did not go inside, but asked her to check to see if the football game had started yet. Not something a kid who was suffering from terror would ask. Sounds like he wanted to know whether he had time to "handle" (Jeantel's word) Zimmerman without missing the kickoff.