A blackjack weapon, also known as a sap, is a type of weapon that is short, concealable, and weighted. It is typically made of a leather pouch or flexible shaft filled with lead powder, molded lead clay, or lead shot to increase impact force. The head of a blackjack is usually hollow and contains a dense but loose or "soft" payload that will deform somewhat on impact. Early blackjacks and some specific classifications still found around the world may utilize a solid lead head or some other solid head that is wrapped in a softer material like leather or macramé. The shaft of the blackjack may similarly be entirely flexible, made out of heavy leather or some other woven material or a flexible cutting of wood.

Blackjacks are typically associated with hooliganism and crime, and were used as a primary weapon in the 1920s to beat up rich people and take their money. They are capable of delivering a powerful blow and can cause head trauma and blackouts, but are considered non-lethal.

In summary, a blackjack weapon is a short, concealable, and weighted weapon that is typically made of a leather pouch or flexible shaft filled with lead powder, molded lead clay, or lead shot to increase impact force. It is associated with hooliganism and crime and can cause head trauma and blackouts, but is considered non-lethal.