I do not believe he was either. I believe that he reacted with instincts that he perceived. In a civilized society, a person in this situation would be justifiably scared. A civil person would have either kept talking home, or called 911 instead of some girl. A person with less desirable perspective, would hide in the shrubs and ambush the person following. Then someone will have to explain to me the rationale of knocking the following person to the ground, bashing this head into the concrete. This physical response to being followed is just not acceptable. But I do recognize that a person with an uncivilized perspective of the would would react exactly as Martin did. The consequences speak for themselves.
Assuming for one second that a gun was not in the equasion, Martin would have, at least, been guilty of assult.
It was a tragic that a person was killed, but Zimmerman has a basic right to defend himself, just like you have.