Icepick grip
The icepick grip, otherwise known as the "reverse grip", is a technique used in close range knifefighting, in which the blade protrudes from the bottom of the hand, rather than the top[1][2][3] ("natural" or "hammer" grip) of the closed fist, resembling the way one would normally use an icepick for its intended use; colloquially referred to as the "stabbing" grip.
Up until the late 1980s, the consensus amongst most martial arts experts was that the icepick grip was the mark of an amateur, and that one who chose to attack using such a grip was easily disarmed. This argument was not entirely without merit, as many impulsive and unskilled knife attacks feature a wild downward thrust in which the knife is gripped in this manner. However, many pragmatic martial artists who had actually been attacked with knives (such as James Keating) became increasingly vocal in their assertion that not only is it extremely dangerous for an unarmed martial artist to attempt to disarm a knifefighter, but in the hands of a reasonably proficient fighter (such as Eskrima practitioners), a knife held in this fashion is remarkably fluid and can deliver multiple cuts from a variety of angles simply by manipulating the wrist. Such flexibility of technique make it extremely dangerous to attempt to immobilize the knife hand by grasping the wrist, as it can quickly circle around and do damage to tendons, nerves, or blood vessels.
This grip is best implemented with a double-edged knife (dagger). If a single-edged knife is used, the edge should be facing outwards, away from the knifefighter and towards the target. In the event that a hiltless (sans crossguard) knife is used (e.g. the balisong or sgian dubh), it is advised that one "cap" the pommel with one's thumb to prevent slippage of one's hand up onto the blade upon impact with a solid object (e.g. bone) -- although, as with the much touted "sabre" and "commando" grips, failure to securely wrap the thumb around the grip will result in a greatly increased likelihood of droppage.