For a century, professional baseball players were regarded as entertainers: see ball, hit ball, play in whatever city you are assigned, for whatever salary you are assigned, and keep your mouth shut.
In 1968, as Americans rose to let their voices be heard, so did the ostensibly privileged subset of baseball players.
They negotiated the first collective bargaining contract in professional sports history, under which the minimum salary rose from $6,000 to $10,000, and the weekly spring training stipend was increased for the first time in 21 years. The next year, Curt Flood refused to accept a trade, the first step toward the adoption of free agency.