As soon as Zimmerman
left his vehicle to follow the young adult, he became the aggressor. Regardless of intent, Zimmerman placed himself in a confrontational position by doing so.
By confronting the young adult and putting himself in danger, Zimmerman cannot use 'self-defense' as an excuse for shooting the young adult.
Any of you that have a CCW permit understand the language and trouble you get into instigating a fight.
What probably happened is you have a young adult(Trayvon) in an unfamiliar neighborhood(remember he was staying with the father's GF), confronted by someone asking a lot of questions and moving threateningly. If you are Trayvon, what do you do?
You defend yourself.
The tragedy is that Zimmerman put himself in a position that resulted in the death of another. That's manslaughter.