What does Boxing Day have to do with boxing?
early 13c. (transitive) "force back, drive back," from Old French reculer "to go back, give way, recede, retreat" (12c.), from Vulgar Latin *reculare, from Latin re- "back" (see re-) + culus "backside, bottom, fundament." Meaning "shrink back, retreat" is first recorded c.1300; and that of "spring back" (as a gun) in 1520s. Related: Recoiled; recoiling.
c.1300, "retreat," from Old French recul "recoil, backward movement, retreat," from reculer (see recoil (v.)). Meaning "back-kick of a firearm" is from 1570s.