Martin was a hood rat. He was also a grade-a psychopath, with a long history of skipping school, dealing drugs, robbing houses, and violent behavior. He went back and assaulted Zimmerman with the intent of killing him. Remember, Zimmerman actually obeyed the 911 operator (who incidentally had no authority to tell the guy not to follow Martin) and was waiting by his pickup to talk to the police, when Martin jumped out of the bushes and assaulted him. Zimmerman didn't start the fight; Martin did. There's no legitimate dispute on this point.