On Christmas Eve 1969, Curt Flood, who had been traded by the St. Louis Cardinals to the Philadelphia Phillies, wrote to then-baseball-commissioner Bowie Kuhn asking to be released from his contract. The Reserve Clause, which appeared in every MLB player agreement, allowed the team to renew a player indefinitely.
Flood had definitely been impacted by the civil rights movement of the 1960s, and believed the Reserve Clause was tantamount to slavery. As he told Kuhn in his letter, “I do not feel I am a piece of property to be bought and sold irrespective of my wishes.