I once was in 'security' at assemblies. They always told us not to tackle any who showed violence. Not even to knock the gun out of his hands - just surround him and force him out of the area.
I never got that - someone with a gun or bomb, and we were supposed to 'passively restrain' him.
I knew that if I ever saw a gun I would tackle the guy. I know that those bullets are real!
Jeff