Within a split second a trained attacker could lunge the blade between your ribs, throat or any other part of your body, even your hand.
If you try to jump backward, you would not have the time and if you try to turn to the side, he could stab again to the side immediately without even moving his body after he landed on the first lunge.
The long blade provides an extension to the hand and the tip of the blade provides immediate control and reach at the same time he lunges forward.
Therefore you need to execute the most efficient defense to this most efficient attack and consider how to limit his follow up options with an additional stab or a follow up hand strike or a kick.
Currently there is no other Self Defense or Martial Art System that has the most efficient answer to this attack but Pure Krav Maga! It is unlikely that anyone else would come up with a new solution either because there is only one most efficient way to attack and only one most efficient way to defend.
Of course you could end up in a different angle and you will have to adjust, but considering the theoretical equation of efficiency, the front stab and the Pure Krav Maga respective defenses are the most efficient attacks and defenses available for the human body!
While the straight stab provides immediate contact with the tip of the blade upon closing of the gap, the slash would be a whipping of the blade to the side of the throat with minimal projection, as the stance would be higher than the straight stab. As the opponent lunges he would bring his hand a little backward over his head around the ear area to gain slashing momentum.
The attacker could also walk with his hands behind his back and throw his arm in a slashing motion as he gets within range.
The third in hierarchy of danger is the circular attack bottom up using the rear hand, and the forth is top down using the rear hand as well. If the front hand is used to stab in these cases, they are considered less efficient forms of straight stabs. In these scenarios the knife hold is either bottomup or topdown, but the direction of the blade is into the front top or front bottom of the torso.
Other tactical methods of using a knife are based on feinting with the front hand, and using the knife in the rear hand. Two knives could be used to that purpose as well or in a fashion of controlling the periphery with short stabs or slashes.
Straight stab with the rear hand could be sequentially treated like a circular attack with the rear hand. Since the opponent needs to first close the gap and then initiate the stab.
All types of holds in the rear hands should be considered as possible threat for tactical feinting. The way to identify the opponent's intention is in the way and side he moves in. Is he moving fast in walking or running motion? Or is he starting to cut the air with his front and/or rear hand before he gets closer?
If the attacker is assuming you will try to block his knife, he might try and prevent you from doing so with his front hand so he can keep stabbing you with his rear hand.
Pure Krav Maga Knife Techniques