A sap is an entangling weapon. It is essentially a rock curled into a cloth rag. Used primarily as a stun weapon, the sap is not a very common item. It deals D4 nonlethal damage. The sap may be used to knock out opponents wearing only leather armor or less. When used by an assassin, any hit knocks out an opponent; for anyone else any hit stuns and 4 or more points of effective damage knocks out opponent.
Source: Dragon Quest Frontiers