How to Bring Your Face to a Sword Fight

Parrying Unarmed Attacks GURPS Basic Set Campaigns p.  376 says:

Parrying Unarmed Attacks: If you successfully parry an unarmed attack (bite, punch, etc.) with a weapon, you may injure your attacker. Immediately roll against your skill with the weapon you used to parry. This roll is at -4 if your attacker used Judo or Karate. If you succeed, your parry struck the attacker’s limb squarely. He gets no defense roll against this! Roll damage normally. 

This rule has some problems. It's actually pretty vague about what kind of damage you do (normal damage, duh) and it can result in some silly outcomes and degenerate tactics.

The Wolf Processor

Using this rule as written, when faced with unarmed opponents who insist on attacking, GURPS players often simply choose All Out Defense (Increased Parry) each turn and then allow their opponents to commit suicide by repeatedly inserting hands/feet/face into sword. This is, if the enemy does insist on attacking from the front or weapon side, a fairly low risk and effective tactic. You can also retreat for +1/+3 from one attack and get back out of Close Combat.

This however, feels cheesy, makes unarmed enemies (at least non-Judo/Karate using enemies) pretty ineffective, would look terrible in a movie, and doesn't lead to any tactical choices other than spamming one maneuver (and thus is boring). 

But, Does it Blend?

That said, could it still be realistic?

I've not done a lot of training in armed defenses against unarmed attacks. Usually I've trained with weapons against weapons or unarmed against unarmed. I've also done very little training for fighting giant badgers. 

I did do some of this with knives and rifle in MCMAP and a lot more when I did a PSD (Personal Security Detail) class. I would say that there are some things you do in these situations that do look a lot like All-Out Defense, but it's not the whole or even the most of it. Mostly what I learned is that you don't want to screw around and risk getting overpowered or disarmed, so you really do want to be more aggressive than just all defense. 

I've also done some training the other way, unarmed versus a knife or gun (since that's how partnered training and sparring works) and learned some disarming or neutralization techniques for this situation. Typically these are risky maneuvers, and there's a reason why most serious self-defense instructors would tell you that escape is your best chance of survival. Despite this, it is still possible for a trained fighter to take your weapon. Of course this would all be Judo or Karate in GURPS and inflict the -4 penalty.

While you certainly might get lucky and stab them right through their the fist, a lot of weapon parries aren't going to do that. One sentence in this rule in particular is both potentially vague and very dubious: "Roll damage normally." Which "normal" damage, exactly? For a weapon with different attack modes, like a sword, is that a normal swing or a normal thrust? 

Almost no armed parry I've ever learned is a full extension swing and for hafted weapons most defenses are with the haft, not the head. It is however reasonable that some armed parries can damage a limb or snoot. 

The Most Normal Damage

My first fix for this is to define what "normal damage" means here is as:
For blades: thr+n cutting, where n is damage adds for the normal cutting damage mode (e.g. if it normally does sw+3 cutting, you do thr+3 cutting). This represents an edge parry against the attacking body part.

Even more realistically, if you want the bookkeeping, you can subtract the weapon's longest reach from this damage, to a minimum of thr+1 (because you aren't using the full leverage of the weapon).
For almost everything else: Thr+1 crushing; you are parrying with the haft or guard.

But, you ask, what if I do want to try to stab his fist with my knife or parry that snoot with my halberd's blade? For that you could allow the following option:

To do impaling (or cutting) instead you can take an additional penalty on the skill roll: -2 + -4 x (longest reach in yards). This does either the weapon's normal thr imp damage, or thr based cutting damage (as for blades above). The Close Combat technique (GURPS Martial Arts p. 69) can reduce this penalty (up to -2 plus half the reach-based penalty).

Save Our Snoots

Where this rule makes sense the most is in the situation where some big angry guy with DX or Brawling is stupidly trying to punch an armed defender. Where it, in my experience, actually comes up the most is when the player characters are being attacked by non-sapient animals or monsters. Here it makes less sense. Even worse is that if the attacking creatures are biters, this free hit goes to the face. Most predators do not know Judo or Karate but probably do know how to bite and protect their heads at the same time.

To address this:

If the attacker is a biter with Sharp Teeth, Sharp Beak or Fangs,  the skill roll is also at -4 plus any levels of Born Biter (GURPS Martial Arts p. 115) (e.g. a canid with Born Biter 1 would give a -3 to this roll). If the roll succeeds, roll 1d, on a 1 you hit the nose (1 or 2 if the attacker has any level of Born Biter) otherwise you hit the jaw.

Ambush Predators and Pack Hunters

The other thing that animals don't often really do is attack armed humans head-on.

Solitary ambush predators, such as big cats, are likely to not attack at all if the they can see their opponent is looking at them, and prefer to pounce (B372) as a surprise attack on unaware (and thus Stunned) prey. If detected, they'll usually back off, and either stalk while waiting for a better opportunity or find easier prey. If cornered and forced to fight against an aware opponent, these animals will usually try to circle around to the undefended side before attacking.

Pack hunters like wolves (or cinematically clever but misnamed utahraptors) will employ distraction tactics. One or more individuals will stay just out of reach, presenting a threat, while the others will try circle around behind the target to attack. Using the Teamwork perk (GURPS Power-Ups 2: Perks p. 8), animals in the distraction role will feint and transfer the benefits to an attacking packmate. If the target turns around to face an animal behind them, they will instinctively switch roles; hunters now behind the target will attack the exposed back or side hexes.