Frank, the event took place in New Jersey.
We here in Manhattan had our own problem in the 1983 Diana Ross concert in Central Park. I crewed the load-in on what was supposed to be the one and only concert but a violent storm cut it short. I live right near the park so I just walked home. Later I got a call that there would be another concert the next day, I declined the crew call as I intended to go to the beach.
Just as well, the "natives" got their act together and there were roaming gangs of thugs robbing and beating concertgoers after the the show. To be blunt, black oriented events -always- require above-average security. That is why "hip-hop" events were not held in the park till just a few years ago and confined to the relatively small Summer Stage space -which is easily policed.
By contrast, there will be the two annual NY Philharmonic concerts on the Great Lawn next week. I go to these every year and they attract approx ten times the number who can fit into the Summer Stage space. There are normally no arrests and no violence.
LCG