ground ball vs roller

ground ball and roller both are nouns.

Word	Noun	Adjective	Verb	Adverb
ground ball	Yes	No	No	No
roller	Yes	No	No	No

As nouns, roller is a hyponym of ground ball; that is, roller is a word with a more specific, narrower meaning than ground ball:

Other hyponyms of ground ball include chop, chopper.

ground ball (noun)	roller (noun)
(baseball) a hit that travels along the ground	a grounder that rolls along the infield
	Old World bird that tumbles or rolls in flight; related to kingfishers
	pigeon that executes backward somersaults in flight or on the ground
	a cylinder that revolves
	a mechanical device consisting of a cylindrical tube around which the hair is wound to curl it
	a small wheel without spokes (as on a roller skate)
	a long heavy sea wave as it advances towards the shore