English▸ verb
(naps, napping, napped)
[no object] (of a horse) refuse, especially habitually, to go on at the rider's instruction; jib: horses which nap should be dealt with by professionals.
– ORIGIN 1950s : back-formation from nappy, an adjective first used to describe heady beer (late Middle English) , later used in the sense ‘intoxicated by drink’ (early 18th century), and since the 1920s used to describe a disobedient horse.