Originally Posted by
duffer1960
The momentum of the bike working through the chain could cause an injury to foot, leg, or ankle, or cause a fall. When the rear freewheels, the momentum to continue only comes from the chain, crankset, freewheel, and your legs, and the worst that happens is you tear your pants.
The rear sprockets do freewheel, though. It's a safety feature. Each sprocket has a couple of spring loaded pawls. They turn stiffly because they are sandwiched together with nylon bushings and don't have a bearing to ride on, but they will turn. They are retained on the hub by a spring and circlip so the pressure clamping them together doesn't get too high to allow movement.