Rooivalk, as a police officer, I am telling you that Martin or any other citizen has a right to follow any suspicious person in their neighborhood and yes, even ask them what they are doing or who they are. The person being asked has no legal obligation to answer. Absent a private peace disturbance (fighting words) directed at the suspicious person, they don’t have right to assault the questioner.
There is no evidence that Zimmerman said any fighting words, but there is evidence that Martin attacked him anyway.
They cannot physically detain them (citizens arrest) unless they have personally seen them commit a crime, usually a felony.
Zimmerman was a volunteer with nothing that was legally binding in his “job” as neighborhood watch captain other than the normal laws any one of us is bound by.
A dispatcher has no legal authority to tell ANYONE what they must do.
If Martin ran away from Zimmerman, he can easily argue that he only ran after Martin to observe his route of travel and destination, not to detain or confront. That is still WATCHING.