kettling

Noun

• 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.
• The situation where water gets trapped in the heat exchanger of a boiler (e.g. due to limescale build-up), resulting in knocking sounds as it turns into expanding steam.

Verb

• Present participle of kettle