fielder vs infielder

fielder and infielder both are nouns.

Word	Noun	Adjective	Verb	Adverb
fielder	Yes	No	No	No
infielder	Yes	No	No	No

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

fielder: a member of the baseball team that is in the field instead of at bat
infielder: (baseball) a person who plays a position in the infield

Other hyponyms of fielder include outfielder.

fielder (noun)	infielder (noun)
a member of the baseball team that is in the field instead of at bat	(baseball) a person who plays a position in the infield
a member of the cricket team that is fielding rather than batting