pro vs free agent

pro and free agent both are nouns.

Word	Noun	Adjective	Verb	Adverb
pro	Yes	Yes	No	Yes
free agent	Yes	No	No	No

As nouns, free agent is a hyponym of pro; that is, free agent is a word with a more specific, narrower meaning than pro:

pro: an athlete who plays for pay
free agent: (sports) a professional athlete who is free to sign a contract to play for any team

Other hyponyms of pro include semipro, semiprofessional.

pro (noun)	free agent (noun)
an argument in favor of a proposal	someone acting freely or even irresponsibly
an athlete who plays for pay	(sports) a professional athlete who is free to sign a contract to play for any team

pro (adjective)	free agent (adjective)
in favor of (an action or proposal etc.)

pro (adverb)	free agent (adverb)
in favor of a proposition, opinion, etc.