They are all just hanging around. Nothing to do, nowhere to go, nobody wants them. Rioting is exciting and is something to do.
No these guys are hired thugs that flew into town to cause a news story. They are professional agitators who get some locals to carry things too far. It only takes a few agitators to create a mob and get it to do things that the mod would not normally be so bold to do. You see it with the police cars. Were some agitators are telling others to roll the police car. Agitators throw the first rock. They yell to the crowd to smash the windows, they may smash the first one. But they are the ones covering their faces.
In Chicago last summer. They were in a crowd near the back. They pushed the crowd toward the police, hoping to get a police reation. The crowd was caught between the agitators in back and the police in front. Fortunately the police were ready and started to go at the back. They did not over react.
In London two summers ago during a large peaceful union demonstration a group, maybe 50 agitators came with masks and hammers and spray paint. The police formed a 30 policeman circle. And as they identified agitators they would throw them one by one into the circle. The agitators could not leave the circle until they removed their masks and showed id. Some were arrested anyway if they were caught in the act.
Agitators are trying to create a news story. Its all marketing really. They want the reporters to get pictures of burning cars and broken windows. They love video of police beating up people.