ballplayer vs pitcher

ballplayer and pitcher both are nouns.

Word	Noun	Adjective	Verb	Adverb
ballplayer	Yes	No	No	No
pitcher	Yes	No	No	No

As nouns, pitcher is a hyponym of ballplayer; that is, pitcher is a word with a more specific, narrower meaning than ballplayer:

ballplayer (noun)	pitcher (noun)
an athlete who plays baseball	the position on a baseball team of the player who throws the ball for a batter to try to hit
	an open vessel with a handle and a spout for pouring
	(baseball) the person who does the pitching
	(botany) a leaf that is modified in such a way as to resemble a pitcher or ewer
	the quantity contained in a pitcher