playing field vs piece of land

playing field and piece of land both are nouns.

Word	Noun	Adjective	Verb	Adverb
playing field	Yes	No	No	No
piece of land	Yes	No	No	No

As nouns, piece of land is a hypernym of playing field; that is, piece of land is a word with a broader meaning than playing field:

Other hypernyms of playing field include parcel, parcel of land, piece of ground, tract.

playing field (noun)	piece of land (noun)
a piece of land prepared for playing a game	an extended area of land
the circumstances under which competition occurs