Hit Location Penalty to Grapple Weapon Hand or Arm

[Captain Joy]

Originally Posted by B370

Grabbing
You can grab something a foe is holding, like a weapon. To do so, you must have an empty hand (but some weapons, such as whips, can also grab). Make an attack using DX or a grappling skill, with the usual penalty to hit the hand (-4).

Originally Posted by B370

Grappling
To grab another body part, apply half the penalty given under Hit Location (p. 398) to your roll…

Question: given a foe with a sword in his hand, what is the penalty to grab that hand? that arm?

I’d always been invoking the halved hit location penalties for grappling, so -2 for the hand and -1 for the arm regardless of what if anything is held in the foe’s hand. But person’s more knowledgeable than I (Douglas Cole) have convinced me that halving the grappling hit location penalties assumes you’re not having to deal with avoiding a dangerous weapon connected to the hit location in question.

As this question comes up fairly often, I thought I’d solicit the wisdom of the GURPS forums.