pop-up vs fly ball

pop-up and fly ball both are nouns.

Word	Noun	Adjective	Verb	Adverb
pop-up	Yes	No	No	No
fly ball	Yes	No	No	No

As nouns, fly ball is a hypernym of pop-up; that is, fly ball is a word with a broader meaning than pop-up:

Other hypernyms of pop-up include fly.

pop-up (noun)	fly ball (noun)
a short high fly ball	(baseball) a hit that flies up in the air
a store that is open for a limited period of time on temporary premises
a book (usually for children) that contains one or more pages such that a three-dimensional structure rises up when a page is opened