The rejected evidence appears to be a desperate attempt by the defense to paint Martin - who was armed only with iced tea and a pack of Skittles at the time of the shooting - as a threatening hoodlum who deserved to die.
Per media accounts of the case, George Zimmerman actively pursued Martin, even though the police, in a 911 call, had told him not to. It was only after continued aggressive pursuit - against police instructions - that Zimmerman confronted Martin and ultimately shot him to death.
That's aggression on Zimmerman's part, not Martin's. You can't pick a fight and then try to put all the blame on the victim when things go awry. Zimmerman could have just gone home when the cops told him that his vigilantism wasn't necessary.
Opening arguments in Zimmerman's trial - in which he is charged with second-degree murder for killing Martin last year - are scheduled to begin on June 10. The trial will surely be an interesting one.