Not yes, but Hell Yes!
So the wounds to Zimmerman don’t make it an open/shut case.
Absolutely, that's why a very thourough, unbiased investigation should be conducted.
Also, once (or if) Zimmerman became the aggressor (by approaching the young adult or trying to detain him) he forfeits his “self defense” reasoning.
Here, "aggressor" is the legally wrong word. Assault and battery must occur before either party's right of self defense is triggered. A simple push with no fall won't do (say many Florida judges, not me), but a punch or kick will. That will put the other party reasonably in fear of their life.
Legally, whoever swung first is the criminal.
"Approaching" is also not assault and battery, approaching a person in public without criminal intent is legal (also applies to both parties, Mr. Martin could also approach Mr. Zimmerman legally.)
Law and justice are not the same thing.
Thank you for the great response. Clears a lot of things up. Question on the "agressor" and "swing first" thing. How can it be first thing? If someone comes at me with a bat, I'd attack first? Wouldn't I be alright to do so? What if a bigger guy comes at a smaller girl or kid? Couldn't they do something to protect themselves without the agressor taking the first swing? Just curious. Thanks again for the resonse.