Yes, THROWBACK is a Scrabble word!

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

Is it a valid word?

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

an organism that has the characteristics of a more primitive type of that organism
a reappearance of an earlier characteristic