third sacker vs third baseman

third sacker and third baseman both are nouns.

Word	Noun	Adjective	Verb	Adverb
third sacker	Yes	No	No	No
third baseman	Yes	No	No	No

As nouns, third sacker and third baseman are synonyms defined as:

third sacker and third baseman: (baseball) the person who plays third base

third sacker (noun)	third baseman (noun)
(baseball) the person who plays third base	(baseball) the person who plays third base