Very interesting. If you read the description of where Zimmerman parked his truck and where Martin's father's girlfriend lived and then look on Google Map, it appears from this account that whomever was being chased was running toward Zimmerman's truck, not toward the home. So this would seem to argue that it was Zimmerman being chased, not Martin. If Martin was being chased, why would he run toward Zimmerman's truck?
What this person's account seems to suggest is that Martin confronted Zimmerman and possibly sucker punched him. Zimmerman ran toward his truck, trying to retreat, but Martin pursued and attacked him again, taking Zimmerman to the ground, where the other witnesses saw Martin on top of Zimmerman, beating him.