"person who rides horses in races," 1660s, a specific use of the earlier sense "boy, fellow" (1520s), which is a special use of the Scottish proper name Jockey, a familiar or diminutive form of Jock. Jockey-boots are from 1680s; jockey-shorts "abbreviated underwear for men" is from 1935 (jockey-briefs from 1946).
1708, "trick, outwit, gain advantage," from jockey (n.) perhaps in its former secondary sense of "horse trader" (1680s) and reflecting their reputation. Meaning "to ride a horse in a race" is from 1767. Related: Jockeyed; jockeying.