Zimmerman was told not to follow him, but he did. He went looking for trouble, and he found it.
Nobody had the authority to tell Zimmerman not to follow him. Trayvon assaulted Zimmerman, just like he assaulted a bus driver two days before Zimmerman shot him, Trayvon was looking for a helpless victim, he didn't find one and he paid for his thuggery with his life. I have no sympathy for him, he got what he desrved and who knows what future crimes, assaults, possibly murders Zimmerman prevented by punching this punk's ticket for him.
If you were walking down the street minding your own business and a Black man started following you and scoping you out, what would your reaction have been?
Black, white, hispanic or Asian, my reaction would be the same, be aware of their position and be prepared to defend myself if they seemed ready to attack. Trayvon didn't do this. Like the uncivlized, thug street scum he is, he addressed the problem by attacking someone, just like he addressed the problem of not being alllowed on a bus without paying two days prior to this incident by attacking someone, namely the bus driver for having the audacity to tell him he had to pay his fare.