first sacker vs first baseman

first sacker and first baseman both are nouns.

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

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

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

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