The Bosman ruling is a 1995 European Court of Justice judgment that let players inside the European Union move to another club for no fee once their contract had expired. Before it, a club could hold a player's registration and demand a fee even after the contract ran out.
The case was brought by Jean-Marc Bosman, a Belgian midfielder whose contract at RFC Liege ended and who wanted to join a French club. His own club demanded a fee anyway and, when none was paid, he was left unable to move on the terms he wanted. He took the case to the European Court and won.
The judgment did two things. It ended fees for out-of-contract players within the European Union, and it struck down the quotas that limited how many players from other member states a club could field. Squads across Europe changed shape within a few seasons.
It also handed players and their agents real leverage for the first time. A contract's final two years became the point of maximum pressure on a club, and the modern pattern of renew-or-sell dates from it, as does the free transfer as a serious route to signing an established player.