‘Contact” can start at the point where Zimmerman, in his pickup truck, began following Martin on foot.
Yes you could say that or you could say it started when Zimmerman first say Martin or where Martin started to approach Zimmerman in his vehicle. All of the points could be considered contact. None of them are justification for a physical confrontation.
Once again “What information do you have that justifies one or the other person in the case to attack the other?”