“I do not feel I am a piece of property to be bought and sold irrespective of my wishes,” St Louis Cardinals outfielder Curt Flood wrote to Major League Baseball (MLB) commissioner Bowie Kuhn in 1969. “I believe that any system which produces that result violates my basic rights.”

When Kuhn balked at his request to stay in St Louis, Flood partnered up with Marvin Miller, head of the Major League Baseball Players Association (MLBPA) and former economist for the United Steelworkers of America. Their fight made it all the way to the Supreme Court, and although they lost that battle, they prevailed in the wider war. MLB’s “reserve clause” — which barred players from switching teams — was broken and the era of free agency was ushered in.

There had been multiple attempts to organize MLB before Flood and Miller came along, some of them dating back to the league’s birth in the late nineteenth century. In his book Baseball’s Power Shift: How the Players Union, the Fans, and the Media Changed American Sports Culture, Krister Swanson documents these efforts and explains how the players ultimately prevailed over the owners, winning more control over their pay and working conditions.