The male player was kicked out in round 24 of the 28-round event in Florida after a fellow player noticed him dropping two blank tiles on the floor.
Executive director of the US National Scrabble Association John Williams said the “Scrabble world is abuzz” at the news.
It is the first time a player has been caught cheating in a national tournament.
Williams declined to identify the player on the grounds he is a minor. He described the level at which the player was competing – Division 3 – as on a par with “any great living-room player out there”.
It is believed that the disgraced wordsmith had put the blank tiles – which can be used to represent any letter – aside in order to use them when he might need them most.
The winner of the tournament receives a cash prize of US$10,000.
The player admitted that he was cheating when challenged, tournament officials said.