What does Boxing Day have to do with boxing?
mid-14c., "hazardous" (also "occurring by chance," late 14c.), from Old French aventuros "chance, accidental, fortuitous;" of persons, "devoted to adventure" (Modern French aventureux), from aventure (see adventure (n.)). Sense evolution is through "rash, risk-taking" (c.1400), "daring, fond of adventure" (mid-15c.).