If your mechanism is designed properly, then all of the stored energy will go into the ball. Hopefully the teams trying this will use a smaller force over a longer distance to accelerate the ball, which would mean that there really wouldn't be any super fast moving parts if it fired while a ball was loaded. The real danger is if it fires without a ball to put all of it's energy into, but hopefully teams will design safety features that will (mostly) eliminate this problem.
I really don't see where the danger is if it's working properly. A ball that was thrown over will hit the ground with about the same speed as a ball that was dropped over. Unless we should all be required to set the ball down on the ground for ultimate safety?
