pitcher vs left hander

pitcher and left hander both are nouns.

Word	Noun	Adjective	Verb	Adverb
pitcher	Yes	No	No	No
left hander	Yes	No	No	No

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

pitcher (noun)	left hander (noun)
the position on a baseball team of the player who throws the ball for a batter to try to hit	a baseball pitcher who throws the ball with the left hand
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