All of that after he was obviously following Martin which couldn've elicited defensive behavior; Martin could've been trying to lose Zimmerman because he was scared and didn't want to lead a stranger back to his house where his little brother was.
"Confirmation bias" is where someone has a preconceived notion of a situation/person and then, consciously or subconsciously, looks for only evidence to support that notion. We don't know whether Matin had his hand in his waistband (not proof of wrongdoing), was actually walking toward Zimmerman.
That "chased donw" comment I made was me asking if that's what it takes to justify someone being afraid or feeling threatened by someone coming after them.
The answer is "no," by the way. Zimmerman followed him; since his truck didn't have a a cloaking device built in, Martin probably noticed him and was freaked out. The following doesn't have to be extremely obvious to be creepy, disconcerting behavior.
You first brought up "running him down." I first mentioned "chased down" as a general example.