Whats a "sap"??
I know what an "asp" is but not a sap.
A sap is an antiquated term, but is generally used to refer to portable slapping devices. Typically, a sap is made from stitched leather, and is flexible, with a handle on one end and a lead shot filled cavity at the other. You can cause quite a bit of damage to another human being if you hit him with the full force of a swung sap.
See also: blackjack, slapper.