Shields must be within the constraints of 30″ round. Tower shields must be no wider than your forearm and no taller then the space between your ankle and your collar bone. All shields must be padded around the edges with pipe foam, and no screws, nails bolts or other potentially hazardous things should be protruding. Shields may be made of almost any sturdy material including plywood and plastic.As far as straps go, there are no rules saying you can't have them. Having one that goes around your neck splits the weight of the shield, but it might be a pain in the butt when you have to fall to the ground.