fly ball vs line drive

fly ball and line drive both are nouns.

Word	Noun	Adjective	Verb	Adverb
fly ball	Yes	No	No	No
line drive	Yes	No	No	No

As nouns, line drive is a hyponym of fly ball; that is, line drive is a word with a more specific, narrower meaning than fly ball:

Other hyponyms of fly ball include blast, pop-fly, pop-up, pop fly, liner, flare, Texas leaguer.

fly ball (noun)	line drive (noun)
(baseball) a hit that flies up in the air	(baseball) a hit that flies straight out from the batter