For starters, Serino in his capias request made an issue of Zimmerman not identifying himself as NW.
One of Serino's more laughable comments given the sequence.
TM: You gotta a problem homey?
GZ: No
TM: You do now.
GZ: [turns and reaches for phone, TM decks him]
Serino's scenario?
TM: You gotta problem homey?
GZ: No, I'm with neighborhood watch
TM: Oh sweet, Just went to the store and got some tea and Skittles for my brother and we're gonna watch the game. You wanna come over?
Certainly any number of actions by both parties that could have changed the outcome. By the time TM walked up to George to confront him, I think the outcome was probably determined.