Yes, PENALTY is a Scrabble word!

Letter values in Scrabble US: P 3, E 1, N 1, A 1, L 1, T 1, Y 4.

Is it a valid word?

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

the act of punishing
a payment required for not fulfilling a contract
the disadvantage or painful consequences of an action or condition
(games) a handicap or disadvantage that is imposed on a competitor (or a team) for an infraction of the rules of the game

Not playable in Scrabble US: PENALISATION.