On what grounds? You can't just randomly search a person's locker because you feel like it.
They can pat you down when you enter the ballpark. You are voluntarily giving up rights to see the game.
This would be huge showdown with the union, but I think it's time. Employees have no right to privacy in their belongings at work, do they?
Again, let me know when it's a player on a good team, especially one on a team I give a crap about, and when there's proof it took place in DC.