Yes, KICKOFF is a Scrabble word!

Letter values in Scrabble US: K 5, I 1, C 3, K 5, O 1, F 4, F 4.

Is it a valid word?

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

(football) a kick from the center of the field to start a football game or to resume it after a score
the time at which something is supposed to begin
a start given to contestants

Also: get-go, starting time, send-off, start-off.