1570s, "to strike back and forth," from M.Fr. bander, from root of band (2). The sense apparently evolved from "join together to oppose," to opposition itself, to "exchanging blows," then metaphorically, to volleying in tennis. Bandy was a 17c. Irish game, precursor of field hockey, played with curved a stick (also called a bandy), hence bandy-legged (1680s).