Uses of Reverse Grip
The spear was the basic weapon of warfare for thousands of years. It inflicts damage by thrusting rather than swinging, and can be used with either one or two hands. Underhand is good for most purposes, including thrusting from below or couching it on horseback, but overhand (i.e. reverse grip) is useful for a plunging thrust over an opponent's shield, stabbing down at foot soldiers from horseback, or throwing the spear like a javelin. Overhand is also easier to use in a phalanx or shield wall where you’re restricted by the overlapping shields. One’s grip should change from moment to moment depending on the circumstance.
The quarterstaff or any two-handed polearm that can both strike and thrust can be gripped in one of two ways. The first is a kind of "spear" grip where you hold the shaft with the rear hand near the butt and the lead hand near the middle, with the thumb of each hand in the "up" position. In the spear grip you can either thrust with a "pool cue" motion, pushing with your rear hand while letting the shaft slide through your lead hand; swing with two hands like a two-handed sword; or even make a one-handed swing with the rear hand accompanied by a passing step for maximum reach in striking. The alternative is a "staff" or "Robin Hood" grip where each hand grips the shaft at about the one-third point on either side, and both thumbs point inward towards the center. It allows one to strike easily with either end, and at closer range. For our purposes that’s comparable to reverse grip, yet it is much more practical than reverse grip on a single-handed sword. Neither hand needs the pinky finger for leverage; the thumb joint can deliver the power as long as the fulcrum is elsewhere, so one simply pushes with the attacking hand and pulls with the other.
The dagger has often been used in the “ice pick grip” throughout history. It enables you to draw a dagger sheathed on your right hip (assuming you are right-handed) quickly and at very close quarters. Relatedly, it is easy to hide a dagger in your hand by hooking your forefingers over the butt of the handle and holding the blade parallel to your forearm (hand-hiding sleeves can make this even more effective), from which you can shift your fingers to quickly have it in ice pick grip. Immediately upon drawing you can stab downward into your opponent’s face or chest with a lot of force from your tricep and lat muscles. You can actually stab horizontally from the right or left just as easily, with up from below being the only angle that’s somewhat awkward for your wrist. With the blade pointing down or at an acute angle with your forearm you can use it as a hook for disarms and grappling. You lose some reach compared to the point-up or “saber” grip, but daggers are so short to begin with that it's no great loss. If your opponent also armed with a dagger, and he attacks your hand, you can just move it out of the way. If instead he wants to attack the actual vital targets of your head and torso, then even if he has a longer dagger or is using the saber grip he will have to get close enough for you to possibly intercept his dagger hand. Unlike in sword fighting there is very little blade-on-blade parrying or winding, and many blocks or counters take the form of going for his hand and wrist. There isn’t much need for a crossguard or a long blade if you go dagger versus dagger.
If you have a knife or an edged dagger, you will find it easier to cut using a saber grip. But in any case, knife cuts don’t have much "stopping power" unless you target vulnerable spots such as the throat, face, or hands. You aren’t going to chop off someone’s arm with one swing no matter what grip you're using, because it hasn’t got the mass or angular momentum of a sword. This all means that the difference in cutting performance between saber and ice pick grip isn’t so huge that it would outweigh any potential advantages of reverse grip. The reverse grip allows for a pretty decent forehand slash. You get less effectiveness on the backhand, but you could make that trade off for the options you gain with the point.
A reverse hand grip can be useful when drawing a very long-bladed sword from a scabbard on the hip. However, since the whole purpose of a longer sword is more reach, you should immediately switch to orthodox grip as soon as the blade clears the throat of the scabbard.
Why Reverse Grip is more problematic for swords than daggers
Before we go into the reverse grip, we should examine how the normal sword grip works. To grip a weapon such as a sword or club in one hand, a person can (if they desire) simply wrap the four fingers around it without also wrapping the thumb. This is because primate fingers are long and designed to wrap around objects such as tree branches, something which a pawed animal like a dog would be incapable of doing. The tendency is to start out in a "hammer" grip where the fingernails are aligned more or less vertically, and the weapon shaft sticks out more or less perpendicularly to the forearm. From that starting position you can extend the tip straight out in front of you by transitioning your fingers into the "handshake" grip—making a diagonal arrangement out of the fingernails with the index finger most extended and the pinky finger most contracted—so that the butt or pommel of the weapon grip is squeezed between the pinky fingertip and the heel of the hand, while the upper part of the grip rests inside the curled index finger. The butt of the handle has room to swing backwards really far—to the extent that the grip can be almost completely parallel with your forearm—because there isn’t some kind of extra thumb on the bottom of your hand to get in the way. All you need to do in order to strike a blow is start with the weapon drawn back so the tip is pointing upwards (or backwards, in which case you’ll at least need to squeeze the top of the grip between your index fingertip and your thumb joint if you want to keep your grip without wrapping your thumb), and then swing your arm forwards and downwards while using the momentum of the sword to snap the point into handshake grip extension.
In case you haven’t noticed, though, most people wrap their thumb around a handle when the grip it. The thumb is very important to use a weapon because it not only helps keep the weapon from slipping out of your grasp, but also helps you manipulate the grip and push against it from above/behind, i.e. the opposite direction from the force applied by your other fingers. If you draw back the sword with the tip pointing behind you in order to charge up for a strong blow, the top of the handle will rest in the fork between your thumb and your index knuckle; the inclination of the sword will be controlled in that case by the extension and contraction of your pinky finger against the bottom of the grip. Then, when you swing down the blow, the fork of the thumb joint will serve as a fulcrum for the handle to pivot against while your pinky finger actuates the point of leverage, facilitating a strong snapping blow. If your blow cuts into the target and the material provides resistance, your thumb serves as a backstop preventing the blade from bouncing backwards and allowing you to apply pressure as you pull the cut through the target. If your opponent parries and enters a binding game against you, the thumb grip is what keeps him from pushing your blade backward with his pressure. If a swordsman loses the thumb on his dominant hand, his swordfighting career is basically finished. That’s why you get that scene in Rurouni Kenshin when Kaoru's father breaks the thumb of a wicked student's dominant hand to ensure he’ll never wield a sword again, and when that student returns as the fake Battousai he’s had to spend years re-learning how to wield a sword in his other hand.
If you had your thumb at the bottom of the hand instead of the top, with which to grip the guard end of the handle while you levered the pommel end with your pointer finger, then the reverse grip would make sense. Since that isn’t the case, and you can only use your thumb to grip the pommel end if the sword is in reverse grip, you’ve got the fulcrum at the pommel end and no means of pushing the grip at the guard end. The only way to snap the point to full forward extension when you do a descending strike with the reverse grip is to open your lower three fingers as you swing with your arm and let the guard end of the grip slide to rest on the tips of your extended lower fingers. That technique might allow you to get the kind of extension on the swing you'd with a normal grip, but since you can’t put pressure on the guard end you’ll have no leverage for follow-through if your target proves resistant, and you’re screwed if your opponent binds against your cut because the grip you’ve ended in can’t keep control against pressure. He could easily disarm you or beat you in a bind. Since that option is out, you are instead limited to a kind of reverse hammer grip which does not allow the blade to reach full speed at the end of the cut, and which has shorter reach. Furthermore, you cannot hold an arm-extended longpoint guard at the end of a reverse grip ascending strike because the weight and leverage of a long blade will pull it downward when there’s no thumb to hold it up from underneath. At most you could bend your elbow 90 degrees so the blade would point outward while resting on the heel of your hand, thus subtracting the whole length of your forearm from your reach.
One of the inconvenient things about reverse grip is that it prevents the use of the moulinet, a type of wrist cut that takes the point in a circle from down to up. The initial dropping of the point, which uses gravity to build up centripedal force and can often be used as a hanging parry, relies on the weapon starting and ending in a point-up position. For a bit of extra power you can combine the wrist motion with a slight contraction and extension of your arm. The moulinet is especially popular for swords with handguards such as the knuckle-bow saber or the basket-hilted broadsword, since with a guard it's not as risky to keep your hand presented, and the technique helps you to keep your body protected by the sword. If you try to make a full circle with the blade using reverse grip it simply doesn't work.
Curiously, reverse grip is a bit less awkward when using a sword with two hands. The fact that one hand can act as the fulcrum, and the other the lever, does something to address the issue of thumb positioning. Whereas a sword in one-hand can either be held point-up or point-down, the sword in two hands could conceivably be gripped in four ways, the first being orthodox style with the thumb of both hands facing the crossguard. The second way would be to have your upper hand with thumb facing the pommel plus lower hand with thumb facing the guard, which would give you a pretty strong rising cut from your dominant side into a type of ochs guard. The third way would be to hold your hands with both thumbs facing the pommel, which is the classic way to give a "Coup de grâce" to an opponent who's lying on the ground, and can also be used for unconventional winding. The fourth way would be with the thumb of the upper hand towards the guard and the thumb of the lower hand towards the pommel, but this fourth type of grip probably wouldn't even occur to most people and you can tell it's stupid and unusable the moment you try it: it locks up your wrists and elbows so that the only way to "swing" the sword at all is by rotating your hips, and you are forced to release your lower hand to try something else. So we'll forget the fourth, and say that the second and third are forms of "reverse grip".
