Yes, BLOWBACK is a Scrabble word!

Letter values in Scrabble US: B 3, L 1, O 1, W 4, B 3, A 1, C 3, K 5.

Is it a valid word?

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

the backward escape of gases and unburned gunpowder after a gun is fired
misinformation resulting from the recirculation into the source country of disinformation previously planted abroad by that country's intelligence service