I actually think the leagues can do this and will win in court and here is why.
The leagues are not preventing the players from playing, as the NCAA was doing. Please see the post above from
@bathtubgin.
By doing so, the NCAA was being accused of disparate treatment. The players from the 2022 recrutiing class argued that they had been treated differently than the 2023 recruiting class. And the players were correct. And because the players had never agreed to the rule change and were not even consulted, their only redress is in court.
The other problem for the NCAA is that their decision; recruiting class of 2023 v 2022, is arbitrary. There is no legal reason why the same rule change could not have been applied to the recruiting class of 2022. Add up the arbitrary rule, the disparate treatment and the lack of voice of the players in the construction of the rule, and the players win. Same reasons the players have been winning ever since the Alston case.
Leagues though are in a different legal posture because their members, the schools, agreed upon this rule change and it applies evenly to every school within the league. And the rule is not arbitrary as it applies to everyone regardless of the recruiting class or sports calendar. IMO, no court will tell a league that it cannot punish a league member if the league member violates an agreed upon rule not to use one of these players. In fact the league members may have to go to arbitration/mediation depending on the league contract, so court may not even be an option.
I expect these rules to be challenged because the players have the money to hire attorneys and attorneys like to be paid. And I expect the challengers to lose.