A small wooden club that's roughly 25-30 cm in length. It is often crafted from wood with a sinew-wrapped handle. Some variations has the club head wrapped in leather. As it is normally used in stealth, it is dark in colour to prevent any reflection of light, making it harder to spot.
The blackjack is the weapon of choice for any good thief not wanting to kill anyone, particularly Garrett of the Thief series.