If a crowd gets unruly and starts taking violent action, then the police will switch to a more aggressive attitude. Their actions here reflect the fact that almost all riots are incited and lead by a few individuals who feel strongly or have something to gain from a violent confrontation. The majority of the people present either show up because something exciting is going on or are bystanders who got carried into the mob mentality. Faced with the possibility of arrest or confrontation with police, most of them simply want to escape and go home.
The first step is simple intimidation. Riot officers stand in strict formations and act with military precision. Once they form echelons -- lines of officers that effectively work as barriers -- the officers tap their batons on their shields or stomp their feet in unison. The result can be quite frightening to unarmed civilians -- it looks and sounds as if this group of armed and armored officers is getting ready to come crashing down with clubs swinging. In truth, this display is meant to scare off as many of the rioters as possible without the officers ever getting near them.
Police do not try to arrest every rioter. Their first targets are those who are leading the riot, because often the crowd will disperse without their leaders firing them up and encouraging them. All people who are spotted breaking a law are also targeted for arrest, especially if they injure or kill another person.
When it gets to the point where officers are actually in conflict with the rioters, the goal is still to disperse the crowd. A combination of advancing lines of officers and the use of noxious gas is used to direct the crowd in a certain direction or keep them away from a certain area. The crowd is never pinned down -- rioters are always given an escape route, since the whole point is to get them to run away.
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