little leaguer vs ballplayer

little leaguer and ballplayer both are nouns.

Word	Noun	Adjective	Verb	Adverb
little leaguer	Yes	No	No	No
ballplayer	Yes	No	No	No

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

little leaguer: a player between 8 and 12 years of age who is a member of a little-league team
ballplayer: an athlete who plays baseball

Other hypernyms of little leaguer include baseball player.

little leaguer (noun)	ballplayer (noun)
a player between 8 and 12 years of age who is a member of a little-league team	an athlete who plays baseball