Curt Flood may have been the most influential baseball player in the modern era.  Perhaps for many baseball fans, he might even be a virtual unknown to them. 

Curt Flood was essentially a very good baseball player.  A career that spanned 15 years, most notably with the St Louis Cardinals.  He held a respectable .293 BA and was a Golden Glove outfielder 7 times and a perennial All-Star. 

In 1969, he was traded to the Philadelphia Phillies along with three other players.  This was done without Flood's consent/approval and he simply said "I'm not going".  This may seem like an innocuous act in this present day.  At the time, this simple act of refusal was unheard of and became a controversial event.  In December of 1969, Flood wrote a letter to MLB Commissioner Bowie Kuhn:

After twelve years in the Major Leagues, I do not feel I am a piece of property to be bought and sold irrespective of my wishes.  I believe that any system which produces that result, violates my basic rights as a citizen and is inconsistent with the laws of the United States and of the sovereign States.

It is my desire to play baseball in 1970, and I am capable of playing.  I have received a contract offer from the Philadelphia Club, but I believe I have the right to consider offers from other clubs before making any decisions.  I, therefore, request that you make known to all Major League Clubs my feelings in this matter, and advise them of my availability for the 1970 season.

The request was denied by Kuhn citing the reserve clause and Flood sat out the 1970 season.  A ground breaking lawsuit was filed by Flood challenging the reserve clause.

  Briefly, the reserve clause was part of a standard contract that bound a player to the club that owned the contract. Essentially, the reserve clause violated anti-trust laws and labor laws by limiting a player to one team, restricting competition and maintained market power by ownership. 

The suit Flood v Kuhn climbed all the way to the Supreme Court.  The Supreme court eventually ruled in favor of MLB with the belief that "baseball should stay the way it is". Meanwhile, all other professional sports were not exempt from anti-trust laws.  Why baseball enjoyed immunity from anti-trust laws was not fully explained by the Supreme Court.  This practice was eventually stopped as onslaughts of lawsuits against MLB persisted over the years and free agency and the million dollar baseball player was born. 

It might be safe to assume that Curt Flood would have preferred his career to be better remembered by his accomplishments on the baseball field.  (He did return to baseball but could not regain his All-Star form.)  His impact upon the the game of baseball has reverberated for decades in the form of free agency.