Yes, newmarkets is a Scrabble word!

Noun

1. A long close-fitting coat worn for riding in the 19th century
2. A gambling card game in which chips are placed on the ace and king and queen and jack of separate suits (taken from a separate deck); a player plays the lowest card of a suit in his hand and successively higher cards are played until the sequence stops; the player who plays a card matching one in the layout wins all the chips on that card