Your shirt is obviously an improvised weapon usable for strangling and smothering! Your blood is a liquid, please remove all of it before coming inside! Your shoe is a projectile (remember Bush?) -- you can't have those. Your phone is an artificial noisemaking device, so it also stays out. /s
I'm really perplexed by umbrellas -- so what should people do if it's raining? I'm also amused by "batteries", insofar the word lost its original meaning and is used to refer to single cells too, and by the ban on monopods and tripods, but seemingly not bipods (except they are also improvised bats and projectiles).