A person who Knuckles Under submits and admits defeat. In the drinking taverns of late 17th century London, arguments often raged. If a person wanted to admit defeat, it was customary for him to knock the underside of a table with his knuckle. It has also been suggested that, at a similar time, bare-knuckle prize-boxers would keep their fists down with their knuckles under their hands when they admitted defeat. The phrase has also corrupted over the years to become “buckle under”.