Watching livestreams from demonstrations in my city I saw a lot of this. Local people, mostly guys, were marching and sticking around until the later evening hours to stream live. They were basically patrolling and keeping an eye out for anyone who threw stuff, got out fireworks, or started a fight.
I saw them grab one kid who threw a bottle into a line of cops and chase him down as he ran away. Then when some others began yelling to "kick his ass!" the same guys held anyone back from starting a fight. It was community de-escalation and struck a stark contrast with the gassing and rubber bullets I've seen.
Any time you get a whole bunch of people crammed in together with emotions running high, there's a chance someone will decide to break stuff or punch someone. Seeing the crowd self-policing like this gave me the tiniest bit of hope.