The key idea here is how player movement and contracts changed because of a landmark ruling. The Seitz Rule comes from an arbitration decision by Peter Seitz in 1975 that interpreted the longstanding reserve clause as an antitrust issue and established free agency after a player reached a certain amount of service time. This ended the era where a player was effectively locked to one team for life after each contract expired. After Seitz’s ruling, players could become free agents and negotiate with other teams, dramatically increasing mobility and salaries. The other terms don’t fit this concept. NIL is about name, image, and likeness rights for student-athletes, Speedballs is unrelated to sport contracts, and ProServ refers to a agency, not a rule tied to freeing players from a single team.