Yes, BLOCKERS is a Scrabble word!

Letter values in Scrabble US: B 3, L 1, O 1, C 3, K 5, E 1, R 1, S 1.

Is it a valid word?

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

a football player whose responsibility is to block players attempting to stop an offensive play
a class of drugs that inhibit (block) some biological process

Also: blocking agent.