I lied before when I said that the stick was the oldest weapon - that honour clearly goes to the empty hand.
The man advantage of the empty hand as a weapon is that it's always available. It's also surprisingly potent.
Throws
Then I learned a bit, and one of my instructors laid it out so clearly - a throw doesn't make someone fall down, a throw is throwing someone onto their head. The goal is to bounce the persons head off the ground, stunning them, knocking them out, or killing them. In any case, once they're on the ground, they're (relatively) easy pickings for a neck stomp, sword thrust, or dagger attack.
Throws are some of the most difficult maneuvers to execute (hence the Master depicting throws in Fiore's book is the most ornately dressed), but a proper throw can be devastating.
An example throw, from Fiore:
Here the Scholar (with the gold band on his leg) is depicted in the middle of throwing the student to the ground. The upper arm has disrupted the student's balance by shooting through his centre, and as the student begins to lose his balance, the Scholar "helps" the process along, directing the head down with his upper arm and propelling the student to the ground by grabbing and lifting the leg.
Locks
Locking the arms of all opponents In such a way that none can safely extend their right hand, To show my success I carry a pair of keys in my hand. - Master Fiore Dei Liberi |
There are a couple basic kinds of locks - keys and bars. For an example of a key, extend your arm straight out to the side, then - bending only at the elbow - point straight up. Now, try to rotate your arm at the shoulder to point backwards - you almost immediately hit the end of your range of motion.
If someone were to force your arm back like that, it would be immensely painful. They could apply a great deal of force, likely damaging your arm and almost certainly driving you forcefully to the ground.
The classic bar is the arm bar - this is basically forcing the elbow joint backwards by grasping the hand of an outstretched arm and applying force just above the elbow. Very little force is required to do massive damage to the elbow joint.
Various empty-hand defenses against weapons result in locks, for instance a two-handed defense against a vertical dagger strike can transition into the key I described, or an off-hand defense against a dagger attack from the high left side can be blocked and transitioned into an armbar.
Disarms
In my right hand I hold your dagger, and I gained it through my skill, which is so good that if you draw a dagger on me, I will take it from your hand. -Master Fiore Dei Liberi |
This can arise from an empty-hand defense against an attack, or as a natural result of weapon play.
For instance, if an attack ends with the opponent's pommel in reach, it may be possible to grasp the pommel and twist it against the opponent's thumb, forcing the sword out of their hand while your sword ensures that they cannot land a hit while you're doing that.
An ideal empty-hand dagger defense ends with a disarm - one example would be stopping a blow coming from high on your left side and redirecting their energy past you and twisting their arm down and to your right. Executed properly, your forearm will press against the flat of their dagger and force it out of their hand.
Strikes
I can't find the exact passage at the moment, but Fiore reminds us that we should never forget striking with the empty hand - i.e. punches, kicks, knees, headbutts.
The ideal targets are the soft spots - the solar plexus, the neck, the nose, the groin, or places where great damage can be done - the knee, for example, can be devastated by a kick.
"Dirty" Techniques
Fiore was writing a book of war for people who would be engaged in lethal combat. As such, no effective technique is omitted or disallowed.
Someone choking you? Gouge their eyes.
Someone grappling close? Knee them in the groin (by all accounts, this is very effective regardless of their sex, despite what some may think).
Fish-hooks (digging a finger in between the teeth and the cheek) can be very effective at moving the opponent around, using the principle "where the head goes, the body follows".
Against a bear-hug from behind, grab a finger and twist it backwards until it breaks.
Someone's hand near your face? Bite their finger off.
Someone's face near your face? Bite their nose or ear off.
In a fight where you expect death is on the line, no technique can be rejected as "dirty" or "unsportsmanlike".
Integration with Weapons
I alluded to this in the section on disarms, and several times before, but the empty hand is always available, even when you're holding a weapon. It's totally possible for a winning move in a fight to be dropping your sword and attacking a vulnerable arm with a lock, or dropping your pinned poleaxe and moving in aggressively for a throw.
Summing Up
The human body is a very potent weapon with the right skill and training. I definitely know people that in a hypothetical fight to the death, I would not bet on me even if I had a sword and they did not, such is their skill at unarmed combat.
I also can't overstate how disorienting, painful, devastating some of these techniques are even in a friendly environment.
The empty hand - the first and last weapon of humanity. Don't underestimate it.