The Touch-kill Question
There is a belief in some SCA kingdoms that rapier fighters should call any blow that touches them: “If you feel it, take it." or “There is no such thing as a light blow.” Unfortunately, this directly contradicts the Society Rapier Rules, which say in part:
"In rapier combat, blows will be counted as though they were struck with a real blade, extremely sharp on point and edge. Any blow that would have penetrated the skin shall be counted a good blow. Any blow that strikes a mask, helm or gorget shall be counted as though it struck flesh. Kingdoms shall not alter this standard.”
The crucial element there is “Any blow that would have penetrated the skin shall be counted a good blow.” So the question is: what does it take for an extremely sharp blade to penetrate skin? Fortunately, we have some good scientific data to answer this question.
In 1976, Dr. Bernard Knight, a British forensic pathologist, published an article entitled "Some Medicolegal Aspects of Stab Wounds" in Legal Medicine Annual, which dealt with this precise question. Dr. Knight used a kitchen knife mounted into a spring-loaded handle on human cadavers during routine autopsies to determine the amount of force needed to penetrate the skin.
He found that if the point of the knife was placed against the skin, and pressure was applied gently, that it took about two kilograms (approximately four pounds) of pressure before the blade would penetrate. He also observed that “During the slow isometric application of pressure to the skin, the latter would dimple and the indicator gauge would rise to a threshold point when there was a sudden release of pressure, the knife plunging through the underlying tissues with no additional force. When a knife was pressed with only a single finger, the passing of this threshold point caused the knife to suddenly penetrate deeply into the body, even though the operator attempted to remove the pressure as soon as the loss of resistance was felt.” and that “During the experimental work it became apparent that the skin was by far the most resistant tissue, apart from bone and calcified cartilage. Once the knife penetrated the skin no further force needed to be applied to cause rapid penetration of the tissues beneath the skin.”
He found that the two most important factors in ease of penetration were the sharpness of the blade (which makes sense) and how fast it was moving. Quoting Dr. Knight again: “However, when a more realistic reenactment of the stabbing situation was simulated with a rapid lunge at the skin surface, a dramatic alteration of the usual result was seen. With the knife traveling at several feet per second, penetration occurred so readily that no reading was recorded upon the scale of the instrument. This was attributed to the inertia of the spring system, so that the knife did not begin to move relative to the handle of the apparatus before deep penetration was achieved.”
So how do these elements apply to calling blows in SCA rapier combat? First and foremost, remember that once a blade has hit with sufficient force to penetrate skin, it doesn’t really need more force to penetrate and cause damage. The notion that a blade would only penetrate half an inch past the skin surface is pretty unlikely—if it has the force to penetrate at all, it’s going to go deep.
But there is that “threshold point” for penetration that Dr. Knight described. Most hits in combat are going to exceed that threshold without any trouble, but there are times when you're at the extreme end of your opponent's reach, or he pulls the shot before it lands with any force, or you're moving back as the blow lands, where you may feel the point touch you, but a real blade hitting like that wouldn't have done any damage.
There is a difference between the amount of force required to feel a blade through clothing, and the amount of force needed to put a sharp blade through human skin.
Try this experiment: Take a sharp knife (an X-acto knife is excellent for this) and gently touch the point of it. Can you feel it touch your body?—presumably—has it penetrated and drawn blood? —probably not. This "touch" can be felt, but it obviously isn't doing any damage. Now press gently on the point. Your skin will dimple in around the point, but it's still not being penetrated.<
"If you feel it, call it" is saying, in effect, that just touching the point of a knife will do the same amount of damage as hitting your finger full force with the knife. Sorry, I don't buy that.