"meat of a hog's hind leg used for food," 1630s, from Old English hamm "hollow or bend of the knee," from Proto-Germanic *hamma- (cognates: Old Norse höm, Middle Low German, Middle Dutch hamme, Old High German hamma), from PIE *kone-mo- "shin bone" (cognates: Greek kneme "calf of the leg," Old Irish cnaim "bone"). Ham-fisted (1928) was originally in reference to pilots who were heavy on the controls, as was ham-handed (by 1918). With hammen ifalden "with folded hams" was a Middle English way of saying "kneeling."

"overacting inferior performer," 1882, American English, apparently a shortening of hamfatter (1880) "actor of low grade," which is said (since at least 1889) to be from the old minstrel show song, "The Ham-fat Man" (by 1856). The song, a comical black-face number, has nothing to do with acting, so the connection must be with the quality of acting in minstrel shows, where the song was popular. Its most popular aspect was the chorus and the performance of the line "Hoochee, kouchee, kouchee, says the ham fat man." Ham also had a sports slang sense of "incompetent pugilist" circa 1888, perhaps from ham-fisted. The notion of "amateurish" led to the sense of "amateur radio operator" (1919). The verb in the performance sense is first recorded 1933. As an adjective in this sense by 1935.