GURPS melee treatise vol. 1: hit locations

[elglin]

Disclaimer: all the below largely applies to pretty strong combatants (attack 14+, active defense 12+). In the current campaign, it actually applies to all the PC's.

1. Torso (-0 to hit). The default hit location. The major downside (and the incentive to target something else) is that this is usually the best-armored part of the enemy. A quilt/padded jack (DR 1-2) is likely not too much of a concern; however, chainmail (DR 3-4) and especially scale/laminate/segmented (DR 5-6) very much is.
2. Arm (-2). In post-Roman time this is usually completely unarmored (DR 0). For this reason, if, say, a sword hit connects and deals 5 raw damage (actually low for a 2d), it all gets through with the 1.5x cutting multiplier for 7 HP effective damage. As this exceeds, for most humans, 1/2 of their total HP, that's both a crippling injury (the opponent drops the weapon and the arm is useless for the remainder of combat) and a major wound, which starts the "GURPS death spiral".
3. Leg (-2). Once again, either completely unarmored or (with greaves) about 1/3 armored. As above, a connecting hit usually cripples the leg (and scores a major wound) - only the opponent falls now, getting a nice -3 (or -2 after changing posture to sitting) to active defenses.
In short, an arm hit makes the opponent useless in combat, but he can RUNAWAY. A leg hit removes that opportunity and increases the chance of killing the opponent at the cost of leaving him a modicum of combat value.
4. Neck (-5). With things like aventails and bevors not expected for centuries, this is also completely unarmored. The to-hit penalty will have to be offset with something like a Committed or Telegraphic (if the opponent has no active defenses for whatever reason); however, the damage modifier is x2 for a cutting weapon, and thus an average (for a 2d) damage roll of 7 would drop an opponent to negative HP which is a major wound and an unconsciousness roll.
5. Face (-5). Helmets with substantial cheek protection, like later bascinets or barbutes, as well as all heavy Roman helmets with cheek guards have this location armored against swinging hits. Thrusts (with their lower damage) get an unarmored target. Once again, an attack option will have to be used to offset the to-hit penalty (e.g. an All-Out Attack from a spear-wielding fighter in the second rank who is out of opponent's reach and hence can forgo own active defenses).
The upside is that when a hit to the face is a major wound (as low as 3-4 impaling and 4-5 cutting raw damage), it triggers the "death spiral" at a -5 to the roll. And, drum roll, just about any damage still causes the stun roll, although unmodified.
6. Vitals (-3). This requires impaling damage, limiting this to thrusting attacks with their lower damage. The upside, like with the face, is the "death spiral", which will often be at -5 by just 2 raw damage due to the x3 multiplier. However, this likely won't work against decently-armored opponents.
7. Other hit locations. Feet and hands are at -4 to hit and are usually no worse armored than arms and legs - so you're better hitting the arms and legs. Skull (-7) with its fantastic x4 wounding modifier and no less fantastic -10 modifier to the "death spiral" is too hard or risky to hit if the opponent has active defenses, is capable of attacking or even has a decent helmet.

To sum it up:
1. Against a lightly armored opponent, attack the torso or vitals (latter preferred with a thrust-only weapon like a spear); consider arms/legs.
2. Against a heavily armored opponent with the usual unarmored locations, attack arms or legs; consider a thrust to the face from the second rank or a cut to the neck if otherwise advantaged.
3. When not expecting a counterattack or when the opponent has no active defenses (i.e. in situations where you can effectively ignore the penalties of All-Out or Telegraphic attacks), and you can thus amass a large to-hit advantage, attack neck or face; or skull if the opponent does not have a (good) helmet.

NB: The "death spiral" so often mentioned above is the Knockdown/Stun roll the injured character rolls when getting a major wound (over half of total HP or crippling a body part - incidentally, the same for arms and legs) or any effective damage to face, skull or vitals. This is an unmodified HT roll which opponents can be expected to fail anywhere from 25% to 50% of the time, and the effect is truly wondrous. The affected character drops prone (-3 to active defenses), drops everything he held (including any weapons) and, until succeeding a further HT roll, is, being stunned, unable to act and at a further -4 to active defenses.
Why is this a death spiral? Let's see:
a. Until the start of your round, you are at a cumulative -7 to active defenses. Which, for most combatants, means no active defenses. Any comrades of the attacker get a free pass on you.
b. If you succeed with the recovery roll, you are still at -3 (because you are prone) to active defenses. Additionally, you are out of Parry (you've dropped your weapon) and possibly (if your shield has a central grip rather than enarmes which is pretty frequent in Dark Ages Europe) out of Block and shield defensive bonus. Dodge at -3 is quite likely 5, which is a 5% success rate. You are pretty much screwed for this round as well. And you've missed your attack. So even if your attacker did not have comrades, he's having a go on you.
c. On the subsequent round you can go from prone to kneeling/sitting and grab your nearby-lying weapon. You are at -2 for active defenses, but you now have your Parry and with an All-Out Defense you can just about offset the posture penalty - at the cost of missing an attack.

The overwhelming likelihood is that somewhere between a) and c) inclusive, most often at b), you are getting another hit, restarting the cycle if not bringing you to negative HP with their marvelous HT rolls against unconsciousness every round.
On a final note, a major wound to face or vitals will put a -5 to the roll, which means the success rate drops from 50-75% to 5%-16% for most opponents. Good night, sweet prince.