(動詞/名詞) 以警方人員和車輛所形成的封鎖線將抗議示威群眾包圍隔離在一個小區域;用警戒線封鎖或隔離。kettle 原意為「水壺;有蓋的鍋子」,在此它相當於 cordon 或 cordon off。這個字源自德文的 kessel (即英文的 kettle) 及其變體 einkesseln -- 此為軍事用語,意為「包圍」(to surround)。
kettling (現在分詞/動名詞)。

The anarchists, the police seemed to feel, were such an imminent danger to society that they needed to be 'kettled' — in other words, to have three police vans crawling along blocking their left-hand side, and a tight line of police one behind another on their right-hand-side, to make sure there was no possibility of break-out.

I've seen 'kettling' done even more intensively than this, at a recent Smash EDO protest in Brighton, for example, where the police were lined along the front and back of the group as well as down the sides, and I (walking my kid home from school) was warned to get out of the way as if it was an advancing army, rather than just 50-60 protesters. This small group in the 'kettle' was as resentful as you would expect.
—Bibi van der Zee, "'Kettled' anarchists increase worry for G20 demonstrators," The Guardian, March 30, 2009

Well, all four marches made it to the Bank of England - only to be blocked in by police in what's apparently called a 'kettle'. Nobody's being allowed out of the area in scenes reminiscent of Oxford Circus in 2001.
—"G20 Protests: 'Kettle' At Bank, Climate Camp Pitched," Londonist, April 1, 2009