REAL LAWYER: A Brooklyn Pew: Lawful?

On Saturday July 6th an event called "Freaknik Picnic" held in Brooklyn NYC's Prospect Park (nearly?) almost had a bit of fisticuffs turn into a fatal shooting--and a rather unusual shooting, at that, as it appears to have involved a derringer! With only a very short (~7 second) video clip of the confrontation available, and little news reporting that I was able to find, it's not easy to arrive at any definitively RIGHT ANSWERS about who might have been acting lawfully--or not. ...