football field vs gridiron

football field and gridiron both are nouns.

Word	Noun	Adjective	Verb	Adverb
football field	Yes	No	No	No
gridiron	Yes	No	No	No

As nouns, football field and gridiron are synonyms defined as:

football field and gridiron: the playing field on which football is played

football field (noun)	gridiron (noun)
the playing field on which football is played	a cooking utensil of parallel metal bars; used to grill fish or meat
	the playing field on which football is played