What is "kettling"

n. A crowd control technique, used by police, where a hostile group of protesters or rioters are surrounded and not allowed to disperse, sometimes with the use of temporary fencing to corral and isolate portions of the group.

Kettling (also known as containment or corralling) is a police tactic for controlling large crowds during demonstrations or protests. It involves the formation of large cordons of police officers who then move to contain a crowd within a limited area. Protesters are left only one choice of exit controlled by the police – or are completely prevented from leaving, with the effect of denying the protesters access to food, water and toilet facilities for an arbitrary period determined by the police forces.

The tactic has proved controversial, in part because it has resulted in the detention of ordinary bystanders as well as protestors. In March 2012 kettling was ruled lawful by the European Court of Human Rights following a legal challenge.