A rabbit punch is a blow to the neck or to the base of the skull. It is considered especially dangerous because it can damage the cervical vertebrae and subsequently the spinal cord, which may lead to serious and irreparable spinal cord injury. A rabbit punch can also detach the victim's brain from the brain stem, which can kill instantly. Frequently, the victim doesn't even know the punch is coming.
The punch's name is derived from the use of the technique by hunters to kill rabbits with a quick, sharp strike to the back of the head.