first period vs period of play

first period and period of play both are nouns.

Word	Noun	Adjective	Verb	Adverb
first period	Yes	No	No	No
period of play	Yes	No	No	No

first period (noun)	period of play (noun)
the first division into which the play of a game is divided	(in games or plays or other performances) the time during which play proceeds