I remember walking into an ER one night and seeing an officer staring in wonder at the end of his blackjack. That one had a weight at the end of a spring shaft, the weight was covered with smooth leather.
After a moment I realized the weight was bent, seemed to have encountered a round object and sort of wrapped around it. Turned out to be the curve at the top of the guy's head.
Sap gloves can be wonderful things, wonder where mine went?
Considering that many agencies now specify plastic flashlights, I expect saps are officially forbidden. But might be overlooked in some cases. I wouldn't advise toting one as a private citizen.