kickoff vs kick off

kickoff is a noun but kick off is not a noun.

Word	Noun	Adjective	Verb	Adverb
kickoff	Yes	No	No	No
kick off	No	No	Yes	No

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

kickoff (verb)	kick off (verb)
	commence officially