spell down
To be victorious over someone in a spelling competition (known as a "spelling bee" or "spelldown"). A noun or pronoun can be used between "spell" and "down." A first time contestant, she managed to spell down all 29 other competitors to win the city's 22nd annual spelling bee. He spelled Sarah Thompson with his correct spelling of the word "antidisestablishmentarianism."
spell someone down
to win over someone in a spelling match. Frank spelled everyone else down and won the spelling bee. He spelled down almost everyone.
spell down
v. To defeat someone in a spelling bee: My cousin spelled down 15 competitors to reach the finals. I finally spelled last year's champion down.