What does Boxing Day have to do with boxing?
early 15c., "to throw or cast down," from Old French dejeter (12c.), from Latin deiectus "a throwing down, felling, fall," past participle of deicere "to cast down, destroy; drive out; kill, slay, defeat," from de- "down" + -icere, comb. form of iacere "to throw" (see jet (v.)). Originally literal; the sense of "depress in spirit" is c.1500.