Twitter user @ktlikes sent along part of a tweet from the American writer Molly Crabapple
On January 20, 2017, the day of Trump’s inauguration, police kettled 217 anti-Trump protesters in the freezing cold and arrested them after sixteen hours.
Then he asked a one-word question: “NOOB?” I gathered he was talking about “kettle,” which I have been sadly familiar with over the past year, as a verb meaning (I quote from Lexico.com) to “confine (a group of demonstrators or protesters) to a small area, as a method of crowd control during a demonstration. ‘The plan was to get as close to the protest as possible without getting kettled..'” Lexico designates it as British, and the answer to @ktlikes’ question is yes.
The word first popped up in reference to protests at a G-20 Summit in London in April 2009. At the time, the New York Times ran a blog post on police response that got into the kettling term and concept. It included quotes from a Guardian article which suggested the tactic may have originated in football/soccer crowd control, and that the verb may have come from a noun used by police:
When the main body of protesters arrived on Wednesday from four different directions at their planned destination of the Bank of England, they soon found themselves hemmed in from all sides by ranks of police. Requests to leave the area were refused. This is, in police terms, the “kettle.”
Google Ngram Viewer confirms the British origin:
The graph indicates increasing U.S. use in the 2010s, and in fact the linguist Lynne Murphy chose “kettling” as her 2011 UK-to-US Word of the Year. Ngram Viewer data only goes through 2019, and I would imagine the U.S. would have caught up to Britain by this point. “Kettling” has been used well over a dozen times in the New York Times in the past year, most recently two days ago, in a quote by a Washington Post journalist describing her experiences covering Wednesday’s insurrection:
Law enforcement started kettling, creating circles of police officers around people. I’ve been in those many times, and usually I say I’m a journalist and they let me out. They didn’t in this situation, and I was taken aback. I went to three different officers and said we were journalists. When they didn’t engage at all, I thought we might be in a dangerous situation.
She ended up getting out okay.
notoneoffbritishisms.com 
It is not so much the word that is migrating to the US as the police tactic for controlling crowds. The term itself is of German origin, the word “kettle” being an English translation of the procedure used in Germany, adopted and enhanced in the UK in the late-20th century.
If you had a German or English quote from pre-2009, that would be most welcome. All the evidence I’ve seen points to it popping up in English that year, at least in written sources.
According to the OED, the origin is the same as a kitchen kettle: Old English cetel, cietel, of Germanic origin, based on Latin catillus, diminutive of catinus ‘deep container for cooking or serving food’. In Middle English the word’s form was influenced by Old Norse ketill.
Reading a book on the seige of Stalingrad – the German army were surrounded and locked in the ‘kessel’ or kettle. Sorry, but I can’t recall title or author…
Thanks. Your comment led me to a Ben Zimmer article on the word in the Wall Street Journal in June 2020 (https://www.wsj.com/articles/kettling-from-german-military-tactics-to-u-s-city-streets-11591968294), where he writes:
In German… “kessel” developed on a different track from English “kettle.” While the English counterpart might bring to mind a whistling teakettle letting off steam, the German word more typically refers to a large metal cauldron. “Kessel” also developed a meaning among hunters for a lair of game animals, like foxes or rabbits, which could be closed in on during a hunt.
When “kessel” was brought into military use, that hunting sense carried over, applied to an area where an army is completely surrounded by a larger force. The German army in World War II became known for a battle tactic called “Keil und Kessel,” translated as “wedge and trap” in a 1942 U.S. Army report by an infantry instructor, Carrol A. Edson, who wrote, “the enemy is in the kettle, or as we would say, in the pot, or, more colloquially, ‘in the bag.’” Edson made note of the German hunting usage, deciding on “trap” as the best English rendering.
“Kessel” came to stand on its own for this kind of encircling maneuver (most famously used at the Battle of Stalingrad), and German police would take on the term themselves. A 1986 crackdown on an antinuclear demonstration in Hamburg, for instance, came to be known as the “Hamburger Kessel.”
That fits. Thanks.
Just what I was going to say; I have always understood it to be from the German Kessel. Wikipedia article here: https://en.wikipedia.org/wiki/Pocket_(military)
Small correction: Lynne Murphy chose “kettling” as her 2011 UK-to-US Word of the Year, not t’other way around as it says in this blog post.
Thanks, I’ll correct. There’s about a 50-50 chance I’ll get something like this wrong, and this time it went the other way.
Not a term I’ve ever heard in the policing sense, but the cooking pot definition remains in British usage in the term ‘fish kettle’ (for gently cooking fish) and perhaps the phrase ‘the pot calling the kettle black’, though that could be a tea kettle, of course. And then there are kettle bells for exercising which bear little resemblance to other kettles of any description and kettle drums which are very like cauldrons. Kettling sounds like it should be a baby kettle.