This section is found on page 114 of GURPS Martial Arts.
Doug Cole refers to it in 2016 in http://forums.sjgames.com/showpost.php?p=1987160&postcount=34 when discussing "Changes to All-Out and Committed Attacks When Grappling" from page 22 of GURPS Martial Arts: Technical Grappling
Initially the policy was this:
- Neither All-Out Attack nor Committed Attack prevents you from rolling to keep someone you’ve grappled from breaking free, though, or gives a penalty to such a roll. That isn’t a defense roll!
TG changed this by requiring defense rolls against the Break Free to prevent CP being rolled and subtracted.
Previously the Quick Contest of a Break Free if lost would mean someone instantaneously getting free though. This is no longer the case.
Even though AOA would prevent stopping CP rolls, it's possible for CP to not lower at all if someone's ST is too low: they might roll a 0. That could even apply to those with thrust 1d (can't roll a 0) against foes with Control Resistance, since that new advantage applies against Break Free attempts too (as per handcuffs). This weirdly even includes the CR imparted by Slippery or being bareskinned (CR1) or oily (CR3) even though presumably that ought to make someone EASIER to break free of.
House rule[]
Given that ST as mass is allowed as a passive defense even when using AOA (just at untrained ST-4 instead of effective Trained ST) one might opt to allow Brute Parry (based on ST-4, ie -2 penalty when halved) as a sort of passive defense against Break Free, representing how a Berserker (making AOA attacks) could still maintain a tight grip on his weapon, or the difficulty of unwrapping heavy limbs of an unconscious foe, or lifting a dead body sat atop you.
HP is used as the mass metaphor in slams so substituting that for ST could also be a better rule. It makes a little more sense since HP is not reduced by CP applications like ST is, so people would be less prone to assuming that passive mass defenses would be reduced to lower "effective" numbers by CP penalties.
Given how powerful that is though, it may not be necessary at all! TG9 actually already appears to account for this because it penalizes "attacks to break free if you are trapped under a heavier opponent" using TG8's GEM rules, so also allowing mass-based passive parries against those attacks might risk double-counting.