Why are restrictions on free agency considered legal in sports other than baseball (i.e. those that are not exempt from anti-trust laws)?
The players' union agrees to the restrictions in collective bargaining agreements
They are not legal - leagues have no ability to restrict player movement.
Courts ruled that teams could not survive if every player was a free agent, so the leagues are allowed to restrict player movement.
None of the other answers is correct
An answer with a brief explanation please.