I’m afraid I don’t understand what you’re trying to say here.
The point is that Martin apparently bragged about being involved in violence and others attributed violence to him, as well. This means, at the very least (if he didn’t actually get involved in any violence), that he valued having a reputation as a violent person. At the worst, it means he actually was a violent person. In either case we see a possible motivation for his attacking Zimmerman, an older fatter man he thought was probably harmless to him, a good opportunity to embellish his reputation as a violent person.