Legs have about the same reach of arms. Your most vulnerable pressure point at the end of your reach could be your groin if you are using kicks, or your neck if you use your arms.
Using kicks however, facilitate faster reach to the center of the body area or below to the knee area. Your legs are less coordinated but when covered with a shoe can deliver greater stopping force if done decisively.
In certain scenarios, front kick to the tail bone is used when the opponent is trying to escape initial defense and counter attack when you use your hands.
Basically in Krav Maga Side Kick to the knee is always used when the attacker approaches defender from the side.
Rear kicks could be used and have been used occasionally if you turned your head and noticed someone approaching with a knife behind you. If you are out of time, you can fall forward with a forward rollover, turn as you get up to face your opponent and then kick him.
If the attacker approaches defender from the front then front kicks to the groin, chest or chin would be used or round house kicks to the groin followed with a side kick to the knee after the initial advance and re-positioning to the side of the opponent.
Usually the choice between a direct kick forward or an evasive maneuver slightly to the side as advancing forward followed with a round house kick depends on the accessibility of the opponent's groin from the direction of the defender's escape.
If the attacker's front leg is in the way, then, a round house kick would facilitate a better reach.
Another crucial factor is to provide maximum safety for the kicking leg and ensure it would not kick in the path of a possible blade stab.
You also must consider that your leg will be subjected to a risk depending on the type of footwear you are using.
The most dangerous knife attack is the straight stab using the front hand. The secondary in danger is the slash, which has almost the same range or reach.
While both are quick and deadly, the straight stab gives an experienced attacker the opportunity to start his motion from much greater distance.
While the straight stab provide to an 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.
Well, maybe a little bit projection as the stance would be higher than the straight stab, and as the opponent lunges he would bring his hand a little backward for the slashing momentum.
The attacker could walk with his hands behind his back and throw his arm in a slashing motion as he gets within range.
The whipping's range would be almost as close to linear mode when done with the front hand. Forms of lesser efficiency could be used by the attacker as well.
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.
Other tactical methods of using a knife are based one feinting with the front hand, and using the knife in the rear hand. Two knives could be used to that purpose as well.
Straight stab with the rear hand should be 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 seed 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.
Your defense with kicks countering knife attacks, would be directed to the chin or the chest with the heel executed with the cross leg of the defender to the attacker's knife holding hand.
If the attacker is noticed on time to facilitate kicking, position your body in neutral position if you have the time before the gap is closed preferably in front so you can have a peripheral view and control of the timing.
If you do not have the time you will probably have to resort to defending with your hands.
You need to identify your opponent's course of action before you choose your best method of preemptive kick attack option. The following are the indicators that will point out what your opponent is about to do.
First according to the hold the opponent is gripping the knife. Second according to which hand he is holding it. Third, according to the height and direction the opponent is able to stab from his initial position or as he gets closer as he might attempt to stab or slash various areas in your body, not all the time with the most obvious optimal convenient hold or stance.
Execute the kick to either the head area or the groin area whichever is farther from the knife to avoid a counter move and getting stabbed in the leg.
Remember that when these techniques were developed the soldiers wore a leather boot but the knives used could penetrate a metal oil barrel.
Remember also that a direct kick to the center of the body that hits the opponent chest or even his crossed arms would stop the opponent with the initial impact.
However if the opponent managed to poke your leg with the blade before you kicked him, you probably would not have many chances to continue.
For example the front kick to the groin is tactically executed with the defender’s leg which is across the hand holding the knife, not in front. This forces the defender to move his body slightly to the opponent’s side away from the slightly angular top down direction of the knife.
Another tactical component for example in the response to the straight stab executed most efficiently with the attacker’s front hand. The counter kick would be a round house kick to the groin followed with a side kick to the knee.
The round house kick is being executed as a continuation of the tactical evasive maneuver that is triggered by the instinctive throw of the opposite to the knife shoulder down to the ground and shifting the body weight to the side which causes the body to shift out of the direction of the stab.
But that initial instinctive motion is honed to promote more the timing and force of the counter kick than the complete tactical evasion from the stab. But at least if you are running out of time you are in the right direction to escape.
The Scissors kick tactical maneuver would be lifting abruptly the defender’s leg to below knee height in front of the attacker rear hand holding the knife, then dropping that leg back to the ground to facilitate a lift of the opposite leg while pivoting the torso.
This brings you to execute a jumping kick to the chest or chin very quickly from the spot easily, in the correct timing re-positioning you body slightly away from the linear or circular direction of the blade.
So for straight front hand stab, you will use the respective round house kick to the groin, followed with a side kick.
If it is a very low straight stab you might skip the kick to the groin but instead complete that same tactical evasion and move on to the kick to the knee from the side. For circular top down or horizontal top side you will kick to the groin.
Remember that with circular moves, the opponent first has to close the gap and then to initiate the momentum of the circular stab. So when he starts to close the gap you move in and kick him.
As for bottom up or bottom to the side circular motion you respond with a scissors kick to the chest or chin, depending on the lunging height the opponent is presenting his body to you. You do not want to waist too much time going to a high altitude but rather you want to accelerate forward.
You execute the same last response if the attacker is executing a rear hand straight stab because first he has to close the gap and then he has to initiate the circular stab.
Now what if the attacker is standing in 45 degrees hands crossed over chest blade is pointed out with a top down hold?
He could be waiting to see you move and aim for your leg or arm or advancing forward. He could either be calculated trying to ensure he can continue a series of attacks or lunge with his body and knife in opposite direction which can be a little confusing.
If he lunged and missed he would not be able to stab again immediately with his second hand. But if he is standing forty- five degrees, hands crossed in the center, he can poke or slash forty five degree to either side and attack you from either side.
Well from his position he cannot lunge as far as a frontal position, but if you tried to kick him he could aim for your leg as he lunges. Of course he can just be pinned advancing slowly trying to execute a fast figure eight attack.
The key is the first most efficient capacity form the initial stance, the capacity to point the blade in a defensive poke or cut and the capacity to lunge and then poke or cut with the blade.
So a preemptive kick for someone who you just noticed holding two knives in that scenario would be a kick to the center of his crossed arms. Or a kick to his knee as he advances.
You really never want to project your intention or capability to defend yourself and surprise your opponent. However lets say someone that assumes you are a trained professional approaches you trying to counter your defense, and is actually trying a tactical shadowboxing with his knife or knives.
It would probably be best to wait for him to enter your range with a timing kick and a follow up hands, or wait a split second more and use your body and forearms for defenses.
Let's talk about kicking an opponent which is about to slash you. Well if he is standing ready for a front hand straight stab he might use a slashing motion to deflect your wrist first but his initial motion would be the same as straight stab so you would react and execute a defense vs. a straight stab as discussed above.
But if he is standing with his hand like a barber using a razor, hand in front of his shoulder thumb down now what do you think would be the preferred kick if you are standing in front of him?
Although the motion is angular circular somewhat the blade is pointed forward and not down, and the damage to your arteries is done with the tip of the blade.
This gives the attacker greater range and faster reach forward than it would with a circular top down. Although the attacker can lunge forward and complete his circular motion with his front hand upon entering your territory, that swift motion also contour his body in a twist that might naturally evade a counter kick to the groin.
This is why my preference would be to delay the timing of the kick if you chose to use it to after you throw your upper torso backward to evade the quick slash and try to kick his arm afterward. However, if your torso already dropped down without kicking yet, how much force can you get with the kick now?
This is why I would prefer not to use kicks at all in this scenario!
Finally, remember that the most important response to even be able to get some use of what you learned is the awareness. You need to respond to any attempt of another human to move into your territory appropriately.
Many times you just notice a person falling or jumping into your space, and the blade might not be that flashy in a dark day.
So you really need to hone your skills to potential attack weather the person is holding a weapon or is in a weapon stance position.
Obviously if you are in a lighted bar and someone is holding his fists up calling you names, he is just trying to intimidate you , and will probably not use a knife initially but perhaps he is trained to kick as well and if he is not drunk he might try that.
But again, since he is trying to intimidate you by projecting his attack or perhaps he is trained in a civilian dojo and not in street smarts, so you have so much time on your hands to respond before anything even happens.