Safety precautions for throw-ins.

tbh i have never even heard of/considered disc wheels as a safety item. they have always been to protect the riders own wheels from the ball, not to protect other riders from their wheels.

They also stop you conveniently slotting your mallet in between the spokes while moving. I learnt about that one the hard way, but still i think that comes under 'dont be a dumbass' rather than a reason to make them mandatory.