They do it all the time in Belfast. Even got a name for it. "Recreational rioting". Prods and Catholics organise a riot at an interface area on a Friday or Saturday night. Go out drinking. Get ****ed. Go to the arranged interface. Start lobbing their empty bottles of Buckfast and WKD at each other. Cops turn up. Everyone turns on the cops.
It's an absolute menace. When I was living in Belfast, some weekends traffic would be redirected so you had to take another route home while they dealt with / contained these little scrotes.
one weekend just give the cops machine guns

wont happen again