Making the Cut: Understanding Combative Cutting Dynamics

Simple Semantics

First of all, let’s establish some frames of reference. What we’re talking about is cutting specific tissues of the human body and any clothing that covers them with the highest degree of mechanical efficiency. As such, we’re going to stick with the term “cut.” Although some knife systems insist on overcomplicating things by differentiating between a “slash,” a “chop,” a “hack,” and whatever other contrived terms they might use, we’re going to keep it simple. We cut.

When it comes to cutting, there are two basic physical possibilities: One is that the blade is in motion before it strikes the target and it continues in motion as it cuts. The other is that the blade is placed against the target first and then moved to generate the cutting force. I refer to the first method as ballistic cutting and the second method as pressure cutting.

The Basics

The best way to understand the basic dynamics of combative cutting is to think of cutting a steak or similar piece of meat. It’s also the best way to grasp the concept of pressure cutting, since ballistic cutting doesn’t lend itself well to fine dining. Using your fork to stabilize the steak, you place the edge of your knife against the meat and do two things: you move the cutting edge back and forth while you apply downward pressure. These two actions are the key components of an effective cut with a small knife. If both are not present, you either don’t cut at all or you work much harder than necessary to get the job done.

When it comes to combative cutting, the exact same principles apply. The cutting edge of a knife is basically a microscopic saw. Drawing that edge through the target allows it to work most efficiently. The longer the cutting edge is and the longer it is in contact with the target, the deeper the cut it will produce.

Pressure into the target is also important. If you place the cutting edge on the meat and press straight down, a sharp knife will still cut. However, in that application, the edge is working more like a wood chisel or a wedge than a knife, and the amount of pressure required to cut is excessive. Against “compressible” targets like clothing-covered flesh, it’s unlikely you’ll cause any damage this way. If you apply pressure and then move the cutting edge longitudinally through the target, you’ll be rewarded with a deep, efficient cut. And the first step to doing this reliably and consistently is with a proper grip.

Get a Grip

If you do any research on knife tactics, you’ll find references to many different styles of knife grip. You’ll also get some creative explanations as to why a particular grip is the only method you should use, whereas others are guaranteed to get you killed in a critical incident. If we maintain our focus on the mechanics of cutting, the requirements of a proper grip become very clear.

Again, let’s accept that we’re using a short-bladed knife because it’s legal to carry. Let’s also assume that we’re talking about a ballistic cut that needs to be performed during a very brief window of opportunity. To visualize this, imagine that you’re cutting the flexor tendons on the inside of an attacker’s wrist as he swings a tire iron at your head. To cut those tendons or the forearm muscles that power them effectively, you need to make the most of the short cutting edge of your knife by drawing the entire length of the edge through the target. That means that you must first make contact with the “heel” of the edge—where the cutting edge starts closest to the knife’s handle. The easiest way to do that is by using a natural index: your thumb.

A proper grip places the thumb immediately opposite the heel of the cutting edge and angles the blade at about 135 degrees to the forearm. By guiding the blade with the thumb and maintaining the wrist angle, you cut with the entire length of the edge and maintain pressure into the target throughout the cut.

When you push a button or ring a doorbell with your thumb, you just do it. There’s no need to close one eye or do anything special to “aim” your thumb because you already have the natural, instinctive ability to touch things accurately. To transfer that coordination and accuracy to the use of a knife, grasp the handle of the knife in a natural “hammer” grip with the blade extending from the thumb side of your hand (a “standard” grip). Now, extend your thumb along the back of the blade. You’ll find that the ball of your thumb naturally rests above the heel of the blade—the spot where you want to start your cut. Ignore the knife in your hand, pick an inanimate target (something that doesn’t bleed), and touch it with your thumb. You’ll find it extremely easy and natural to index the heel of the blade.

The other component of an efficient cut—constant pressure into the target—also begins with a proper grip. Beginning with the grip described above, extend your arm and imagine touching something with the ball of your thumb. Freeze your wrist in that position and take a look at the natural angle between your wrist and the blade of the knife. You’ll find that your wrist instinctively settles to an angle of about 135 degrees (45 degrees forward of a vertical plane).

Combined Dynamics

For easy reference, let’s now imagine a vertical cut. If visualizing a target helps, imagine your attacker’s forearm extended horizontally in front of you. Begin with your knife gripped as described above. Pick a spot on the arm and aim at it with your thumb. Your arm will naturally extend, unfolding at the elbow until the heel of the blade makes contact with the target, guided by the thumb just above it. At that point of contact, the angle between your wrist and the blade is a natural 135 degrees or so, meaning that the point of the blade is extending forward at about 45 degrees.

If you now continue the motion of your arm, you will draw the entire length of the cutting edge through the target. As you do, the natural forward angle of the blade will maintain a constant pressure into the target. The resultant synergy of these two dynamics combines the longitudinal motion of the cutting edge with optimal pressure into the target to produce a deep, extremely efficient cut.

A ballistic cut to the forearm muscles/flexor tendons is demonstrated against a high forehand attack.

If we go back to the idea of a thug swinging a tire iron at your head, your goal is to cut the forearm muscles and/or flexor tendons that enable him to close his fist and grip the weapon. To do that, you simply take the above process and alter the plane of motion of your arm to intersect his arm somewhere between his wrist and his elbow. Since he’s swinging at you, his arm will be in motion. Your knife edge, which will also be in motion, will therefore intercept his arm and create a “head-on collision” that increases the power of your cut. Very importantly, the angle of your blade will allow the edge to bite and cut very deeply, yet still “contour” to the target without getting stuck or bound up. Typically this results in a clean cut that goes all the way to the bone, and a smooth follow-through.

The Pressure is On

Although critics of structural targeting with knives are fond of claiming that it requires “surgical precision,” as we can see from the above example, that’s just not the case. If a surgeon considered a margin of error of roughly six inches in either direction acceptable, I wouldn’t want to be his patient!

With that said, sometimes the best way to get the cut you need to stop an attacker is to first control the target and then place the blade. By achieving accuracy before you worry about power, you increase your chances of cutting the parts that matter most. To illustrate this, let’s revisit the tire-iron scenario.

A pressure cut is performed by first stabilizing the target, placing the blade accurately, and then applying pressure to create the cut. Here it is demonstrated against the triceps muscle.

As your attacker swings at you, you drive forward with both hands to “jam” his strike before it gains momentum and power. Your left hand (assuming you’re a natural righty) checks his forearm, and your right fist, gripping your knife, punches his shoulder. These combined actions stop his arm dead and qualify as a tactic called a “shoulder stop.” To take his arm decisively out of the fight, you quickly wrap your left arm over his weapon arm and suck it tight under your armpit, using your back muscles to control and immobilize it. Your knife hand stays right where it was in front of his right shoulder. Once you’ve achieved solid control over his arm and sucked it in tight to your body, slide your knife hand over a few inches so it’s poised at the top of his bicep muscle, right where it meets the bottom of his deltoid. With a proper grip, you’ll notice that your thumb has guaranteed accurate placement and that your blade is angled forward at about 45 degrees over the attacker’s arm.

From this position, stiffen your wrist to maintain its structure, anchor your right elbow tight against your ribs, and bend your knees suddenly to drop your entire body weight on the edge of your knife. This is a textbook example of what I consider a pressure cut—placing the blade on the target and then applying pressure. Since the blade is pre-positioned at a 45-degree angle, the downward pressure of your body dropping creates a shearing effect that combines constant pressure on the edge with longitudinal movement of the edge through the target. The power and wounding potential of this cutting method are devastating.

We’re Just Getting Started

The dynamics of cutting—particularly with small knives—must be understood and mastered to make the most of your edged-weapon tactics. Without such an understanding, you’re literally “going through the motions” without realizing the full potential of your cuts. Because of the importance of this topic, I will explore it further in future PDN articles.

Related Videos

1. Center-Line Knife Carry