Yeah none of those obstacles were present there...don't see how he couldn't have run circles around him without even breaking a sweat...
If there were no obstacles, Martin probably just got tired of running and confronted Zimmerman. (Although I still like my theory about the irresistible attraction between a fat man and a bag of Skittles. . .) That still doesn't tell us who initiated the physical confrontation though, could go either way.
Not running was obviously not the smart thing to do here, but it's entirely understandable. I have a perfect right to be where I am, doing what I'm doing; why should I run?
One thing that's going to be very important is the distance of the shot. If Martin is on top of Zimmerman and then gets up and backs away, and then Zimmerman shoots him, I don't see how any reasonable person says that isn't second degree murder. The distance should be reasonably easy to determine by the amount and distribution of powder burning present. Hopefully the police will be overseen by the FBI to satisfy everyone there's nothing under the table happening.
And to whomever raised the point that the police can't do a blood test on the shooter without permission or a warrant, this should always be pursued when an unarmed person is shot, but especially when it's a kid. Shouldn't be that hard to get a warrant if needed, and if there's no impairment the shooter should be happy to have that proven.