1747, originally a day of military exercise and review (see field (v.)); figurative sense "any day of unusual bustle, exertion, or display" [Century Dictionary] is from 1827.
Entries linking to field-day
field v.
"to go out to fight," 16c., from field (n.) in the specific sense of "battlefield" (Old English). The sports meaning "to stop and return the ball" is first recorded 1823, originally in cricket; figurative sense of this is from 1902. Related: Fielded; fielding.