Martin should have never assaulted Zimmerman, no one is arguing that.
No matter how legal it is, you don't get assaulted, when you don't follow what you perceive to be a suspicious person.
The correct legal term is not assaulted.
The legal definition for "assault" is, "At Common Law, an intentional act by one person that creates an apprehension in another of an imminent harmful or offensive contact.
An assault is carried out by a threat of bodily harm coupled with an apparent, present ability to cause the harm. It is both a crime and a tort and, therefore, may result in either criminal or civil liability. Generally, the common law definition is the same in criminal and Tort Law. There is, however, an additional Criminal Law category of assault consisting of an attempted but unsuccessful Battery."
The legal term for what TM did to Z is "battery"
The legal definition of "battery" is,"At common law, an intentional unpermitted act causing harmful or offensive contact with the "person" of another.
Battery is concerned with the right to have one's body left alone by others.
Battery is both a tort and a crime. Its essential element, harmful or offensive contact, is the same in both areas of the law. The main distinction between the two categories lies in the penalty imposed. A defendant sued for a tort is civilly liable to the plaintiff for damages. The punishment for criminal battery is a fine, imprisonment, or both. Usually battery is prosecuted as a crime only in cases involving serious harm to the victim."
It's a common mistake that most people make.
You are neighborhood watch, you see a suspicious person, now contact the people who are trained to deal with suspicious people. I don't think that is a job for neighborhood watch.
After contacting the police, it is only logical and reasonable for the NWer to continue to watch
where the suspicious person goes and what they do so that the NWer can report it to the police if and when the police show up.