I have to echo what "fed" said...
They were still in use when I started with the department in the early to mid 80's and I've seen them in action.
Flat sap, spring loaded saps, sap gloves....all basically hitting someone with a rock up side their head.
Just a friendly tap and things can go south very quickly. I'd really hate to see the results (or face the media/jury) if it was used in a moment of fear or rage.
Needless to say no one around here uses them anymore.