What does Boxing Day have to do with boxing?
early 13c., "beggar, vagabond," from Old French truant "beggar, rogue" (12c.), from Gaulish *trougant- (cf. Breton *truan, later truant "vagabond," Welsh truan "wretch," Gaelic truaghan "wretched"). Cf. Spanish truhan "buffoon," from same source. Meaning "one who wanders from an appointed place" is first attested mid-15c. The adjective is recorded from 1540s.