1560s, "cause to go down," from down (adv.). Meaning "swallow hastily" is by 1860; football sense of "bring down (an opposing player) by tackling" is attested by 1887. Figurative sense of "defeat, get the better of" is by 1898. Related: Downed; downing.
also potzer, "an incompetent chess player," especially one who doesn't know he is, by 1948, of uncertain origin. OED points to German patzen "to bungle," but notes that, though the form looks Yiddish, there doesn't seem to be such a word in Yiddish.