I agree this is nonsense, but also have concern that what is seen here as 'doing the right thing' for uniformed LEO's is IMHO implicitly endorsing doing the wrong thing for our legally armed citizens.
This steps on the rights of citizens, LEO or not, who are exercising their natural and constitutionally guaranteed rights to bear arms by siding with property owners. The IMHO overly broad application to uniformed LEO is correct in a way - apply it to everyone or to no one. Who says the armed uniformed LEO is indeed legitimate LEO and not a Tango? Who says LEO are any more/less stable at emotionally charged sporting events than anyone else? There are extreme cases for less than stable LEO and non-LEO and it is the extreme cases that are of concern. Also, any time we have 'special considerations' for LEO who are not on duty/in jurisdiction vs citizens it Is discomforting and ripe for abuse.
I don't believe such venues are able to provide effective security, regardless of their policies. I'm not willing to disarm in such environments. Therefore, I simply avoid all such venues and situations whenever possible. It helps that I could care less about ball sports but the broader principle applies.