Responses above to Exclusivity are close but not quite what I meant ...
Pro sports contracts routinely prohibit certain physical activities to prevent injury risk. Not just high-risk stuff like skydiving and motorcycle riding. Many football and baseball players aren't allowed to play basketball.
It's not for the players' safety. It's to protect the teams financially -- the player can be substantially fined and even have guaranteed money voided.
The leagues spend tons on private investigators because players will brazenly lie to keep their money. Example: the infamous Jeff Kent "car wash" incident.
Hard to imagine notorious contract hard-ass McMahon not doing the same for Steveson.
