Yes, TENNISES is a Scrabble word!

Letter values in Scrabble US: T 1, E 1, N 1, N 1, I 1, S 1, E 1, S 1.

Is it a valid word?

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

a game played with rackets by two or four players who hit a ball back and forth over a net that divides the court

Also: lawn tennis.