Yes, FRESHMAN is a Scrabble word!

Letter values in Scrabble US: F 4, R 1, E 1, S 1, H 4, M 3, A 1, N 1.

Is it a valid word?

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

used of a person in the first year of an experience (especially in United States high school or college)

Also: first-year.

Not playable in Scrabble US: FLEDGELING.