One thing to take note of, in most states, if you verbally threaten someone, that is grounds for assault and criminal threats for the person talking shit, and most states allow a retaliatory response. Whether Melvin is guilty of anything stems from what was actually said. If the 1st guy said something along the lines of " I'm going to fuck you up" and then approached Melvin, Melvin is justified in reacting in defense. It doesn't matter if the guy had his hands behind his back or in the air, or wasn't even looking at him. If you make a threat to someone, and then approached them, that person has every legal right to respond in self defense.
The 2nd guy is highly questionable though. Looked like he was just trying to break it up.