base runner vs ballplayer

base runner and ballplayer both are nouns.

Word	Noun	Adjective	Verb	Adverb
base runner	Yes	No	No	No
ballplayer	Yes	No	No	No

As nouns, ballplayer is a hypernym of base runner; that is, ballplayer is a word with a broader meaning than base runner:

base runner: a baseball player on the team at bat who is on base (or attempting to reach a base)
ballplayer: an athlete who plays baseball

Other hypernyms of base runner include baseball player.

base runner (noun)	ballplayer (noun)
a baseball player on the team at bat who is on base (or attempting to reach a base)	an athlete who plays baseball