This might be something that we could call "headline English". We usually use an object in American English too. In fact, I just went to espn.com and found this headline: "Clemson routs Ohio State to advance". You might have seen a section of the website with very little space, so they cut it down to two words. One difference between American and British English is that we treat a team as singular: "That team (it) routs the other team", while your example from British English used the plural, "Manchester United (they) rout Liverpool". On the other hand, if we have a team name, which is almost always plural in American sports, we treat the team as plural, as "they". For example, I believe the team from Clemson are the Tigers, so if we use that name, the headline would be "Clemson Tigers rout Ohio State", not "routs".

Thanks, Dan and Moirawendy.

As a U.S. native speaker I think of "rout" only as a transitive verb. I agree, it's "headline English." However, similar shortened or truncated expressions are seen in other places as well, such as captions under pictures, or bullet point items in a Powerpoint presentation. The general "rule" is that people leave out words if they think the listener can guess them, and in this case the headline writer assumes that people know who Clemson's rival was, and that the listener supplies the missing name and parses the sentence as if it were "Clemson routs OSU." I can't actually find your headline, but I see that the same site also uses headings like "Tigers' defense keys rout of OSU, sets up Alabama rematch." When sentences get shortened, all kinds of ambiguities creep in, of course. (For example, the grammar doesn't tells us whether the "American Cancer Society" is for cancer or against cancer). Headlines assume that the reader knows a lot of context. I remember a Boston Globe sports headline--I'm afraid I don't remember the context--consisting of the single word "DYNASTY!" Some team had just won some important and contested championship. That meant it had won the championship for so many consecutive years that, in the writer's opinion, it was now worthy of being called a sports dynasty. The headline didn't say who had won or what they had won, because apparently the most important thing was completing some number of consecutive years of winning.