Flood was traded from the Cardinals to the Phillies after the 1969 season. For a few reasons, Flood refused to report to Philadelphia. He wrote a letter to Commissioner Bowie Kuhn requesting to become a free agent. The ruling was that baseball was a sport and not a business so it was exempt from anti-trust laws.
Flood didn't play for Philadelphia or anyone else in 1970. After the season they traded him to the Washington Senators and he played on 13 games for them in 1971.
If you aren't familiar with his career look him up. He had 1,861 career hits, 7 Gold Gloves and he was in three All-Star games.
In 1975 Andy Messersmith and Dave McNally won their challenge and free agency changed everything in baseball including the price of baseball tickets and cards.