It cannot be exactly pinpointed when man began to cover his hand with leather for combat protection purposes; records show that the Greeks used a gloved called a cestus in combat competitions which is the equivalent of boxing today where knocking out the opponent was the objective.  The glove was basically leather thongs that were wrapped around the hand, the wrist and a good portion of the lower arm. 

The Romans took this concept further and added metal parts like metal plates and spikes.  The competition also became more lethal, with gladiators using them to fight to the death.

While the brass knuckle evolved into a more damaging equipment with its solid brass construction, the sap glove is comprised of leather and powdered lead or steel. 

With this construction it can be used effectively for punching or slapping (if that is the model required).  The added weight of the steel or lead allows one to hit with more force.  While these gloves can be effectively used as an offensive weapon, the main intent is for defensive purposes.

When striking or punching with an unprotected hand, one can sustain hand injuries like when striking the head or mouth and hitting the teeth.  With protective cover from the powder or shot lead and leather, injury is less likely to occur yet the force of the strike is in no way lessened.  

This same principle is true when one is attacked since inferior strikes from blunt instruments can be blocked or parried with the gloves.  Also if one has a firm grip on a trouble maker this person may attempt to break free by hitting the hand; the hand will be better protected with a leather sap glove and the grip can be maintained. 

This glove is suited in a close hand to hand combat scenario; it has been used in sports, and is most ideal for law enforcement operatives and security personnel.    It is also marketed to the general public as self-defense equipment. The objective of this type of weapon is to try to cause less damage to the parties involved in the conflict.

Be aware that this product is considered a weapon and while not as lethal as other weapons, is capable of causing damage and injury and should be used responsibly.  To be sure that you are in compliance with the law, check to see if this glove is legal in your area.