Yes, COURSERS is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, U 1, R 1, S 1, E 1, R 1, S 1.

Is it a valid word?

COURSERS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a huntsman who hunts small animals with fast dogs that use sight rather than scent to follow their prey
formerly a strong swift horse ridden into battle
a dog trained for coursing
swift-footed terrestrial plover-like bird of southern Asia and Africa; related to the pratincoles