And I did see “Police” on their vest so may indeed be city LEOs...Then again, SS might be blending in and not advertising who they are...Purely a guess...OPSEC?
Good guess on the “blending in” and the H&K.
Someone upstream asked why the .50 cal. bolt would be suppressed. Can you imagine the sound of an unsuppressed .50 cal. in that small area and in the stadium? Probably rupture, or worse, the eardrums of those seated near by.