1) Keeping the peace 2) Otc market for police 3) Reason to use a water cannon 
Riot control refers to the measures used by police, military, or other security forces to control, disperse, and arrest persons who are involved in a riot, demonstration, or protest. If a riot is spontaneous and irrational, actions which cause people to stop and think for a moment (e.g. loud noises or issuing instructions in a calm tone) can be en...
[n] - the measures taken to control a riot
riot control operation noun the measures taken to control a riot