Definitions for free agent
Random House Webster's College Dictionary
a professional athlete who is not under contract and is free to auction off his or her services to any team.
Origin of free agent:
(sports) a professional athlete who is free to sign a contract to play for any team
free agent, free spirit, freewheeler(noun)
someone acting freely or even irresponsibly
(Sports) A professional athlete who is free to play for or sign a contract to play for any team.
A person who acts freely, or without constraint to a higher power.