What does Boxing Day have to do with boxing?
late Old English sott "stupid person, fool," from Old French sot, from Gallo-Romance *sott- (cf. Medieval Latin sottus, c.800), of uncertain origin, with cognates from Portugal to Germany. Surviving meaning "one who is stupefied with drink" first recorded 1590s. As a verb, it is attested from c.1200, but usually besot.