hand foot major wound knockdown stunning
 

The italic emphasis below is mine.

1. Injury over IP/3 cripples a hand or foot [B420-1].
2. An injury that cripples a body part also counts as a major wound [B420].
3. Whenever you suffer a major wound you must make an immediate HT roll to avoid knockdown and stunning [B420].
   • Success: ordinary shock penalties
   • Failure: Stunned, drop anything you're holding, and fall down
   • Failury by 5+ or critical: You fall unconscious
4. After combat you make a HT roll to see how serious the wound is [B422].
   • Success: Full recovery after normal healing
   • Failure: a lasing injury, but ultimately a full recovery
   • Critical Failure: The hand/foot is permanently crippled and you gain the appropriate disadvantage

A red shirt in my Star Trek campaign recently got a harpoon through his right hand. I remembered the first HT roll right after he received the crippling/major-wound injury. He made his HT roll. But, had he failed it, he's really supposed to suffer knockdown? From a hand injury??? Such knockdown seems a reasonable for major wounds to the body or legs, but not arms or hands. (Not sure about a foot.)

I encourage one and all to explain to me why it's realistic for a person that gets shot in the hand to fall down about half the time. Or, if I've got the rules wrong, please enlighten me.

(The player still needs to make his second HT roll to see how serious the crippling injury is.)

Re: hand foot major wound knockdown stunning
 

The "knockdown" is a reaction to pain, not being bowled over by a mighty blow (that's knockback). The rules seem to assume that crippling wounds are as painful as any other Major Wound. Having only ever broken a wrist, I can't compare a crippled extremity to a crippled limb. But it certainly hurt enough to Stun.

It might be reasonable to give characters a slight bonus to resist knockdown caused by crippled extremities, if you feel they should be less disruptive.

Re: hand foot major wound knockdown stunning
 

In my games, I'm planning to houserule that if the stunning check is failed, a knockdown is not automatic, but requires failing another check (with the same modifiers).

Re: hand foot major wound knockdown stunning
 

To echo vierasmarius, knockdown is 'you fall over', not 'you are knocked over' (covered by knockback, collision/slam rules, or various maneuvers) nor 'you no longer have the mechanical ability to stand' (covered by crippling of the legs, feet, or pelvis).

Re: hand foot major wound knockdown stunning
 

I'd say yes, you can be knocked down by a crippling wound to the hand or foot. Your going to have likely broken a lot of the small bones therein and your body is not likely to react well to that. I obtained Mallet Finger in my martial arts class a couple of years ago and had to sit down or I would have fallen down.

Re: hand foot major wound knockdown stunning
 

There are a stupid number of nerves in the hands and feet. That's a lot of little voices yelling, "AHHHHHHHHH!" for your brain to handle.
Crippling is a bit more than a minor sprain or even break. It's a "you injured it to the point of not functioning" problem.

Re: hand foot major wound knockdown stunning
 

People have been known to fall down when MISSED at close range with gunfire. It was a psychological reaction to the expectation of pain on being shot. Basically, a failed Fright Check.

With a REAL harpoon sticking out of your hand? Yeah, what GURPS calls knockdown (and certainly stunning) is quite possible.

You might scale it, though: A failure by 0 means you are stunned but stay standing, a failure by 1 means you drop to your knees, 2-3 you drop to crawling or sitting, and 4+ you fall all the way to lying down, either face-up or down.

Re: hand foot major wound knockdown stunning
 

I spar full contact, no headgear just mouthpeice and MMA gloves. Ive only ever been knockeddown from eyepokes. Its just a reflex I think. If i can fall down from surprise from damage to a little thing like my eye then why not for getting my hand mangled suddenly.

Re: hand foot major wound knockdown stunning
 

I have a messed up shoulder. When it first was bad before they mostly fixed it I tripped and threw my arms out to maintain balance. I didn't fall down because that would have made it hurt even more. But for quite a few seconds my only though was how much it hurt and only movement a sort of swaying twisting motion because of the pain. So effectively a knockdown in terms of taking me out of action.

Re: hand foot major wound knockdown stunning
 

I'm lucky if I don't barf when I break something serious, let alone fall down when the pain hits my head and my knees buckle.