Over on Twitter, Neal Whitman notes that the adjectival phrase knock-on appears twice in the current issue of New Scientist (British) and wonders if it’s “a recent BrE innovation? Just BrE? Just recent? Neither?”
My answer: fairly recent and, until quite recently, almost exclusively British English. The “quite recently” means that for this blog’s purposes, it’s an on-the-radar NOOB. The OED calls the phrase “chiefly” British and defines it as “Being a secondary or indirect consequence of another action, occurrence, or event; knock-on effect n. a secondary, indirect, or cumulative effect.” First citation is from The Times in 1972: “They would be more than willing to move towards a minimum wage of about £20 a week..if they could be assured..that there would be no ‘knock-on effect’ in the differentials demanded by the rest of the labour force.”
As to derivation, although the term (apparently) has a meaning in rugby football, it’s more likely that the adjectival phrase comes out of physics, where it means “Ejected, produced, or caused as a result of the collision of an atomic or sub-atomic particle with an atom.” (“Knock-on protons produced by 3MeV neutrons would not..produce visible flashes.” Nature, 1971.)
Joining in the Twitter conversation, Lynne Murphy reports finding twenty-nine instances of knock-on in the Corpus of Contemporary American English, which boasts of containing 450 million words used by Americans in writing and on the air since 1990. My own search of COCA yielded twenty-seven hits, but that’s close enough for jazz.
At least half of the uses, I would judge, were written in American publications or uttered on American broadcasts by British people. However, fifteen of the twenty-seven have occurred since 2008, and Americans are responsible for a increasing number of these. For example, in 2011, Steve Coll wrote in a New Yorker blog, “The probable knock-on effect of a second Taliban revolution in Afghanistan would be to increase the likelihood of irregular Islamist attacks from Pakistan against Indian targets.” Georgetown professor Charles Kupchan wrote in Foreign Policy this past January, “[Citizens of industrialized countries] also expect their representatives to deal with surging immigration, global warming, and other knock-on effects of a globalized world.” And Annie Lowrey wrote in the New York Times in August: “Mr. Obama’s address coincided with the release of a White House report quantifying education job losses and detailing the knock-on effects, like bigger classrooms and shorter school years.”
The slowness with which the phrase has been adopted here relates, I would say, to the longstanding presence of perfectly adequate alternatives, side effects and unintended consequences, or, more simply, results. But never underestimate the appeal of a NOOB. I predict that knock-on effects will continue and indeed accelerate its ascent.