Joe:
Check out my article on the Biddle method in CQC Magazine for some info on that system. To my knowledge Styers never used the grip you describe... the palm up/knife to the rear stance was used by Fairbairn/Applegate/Sykes. And as Hock has quoted Applegate as saying, the extremely well known picture of Applegate in that stance was "getting ready to stab you" (or somethign to that effect) and not intended to represent an actually fighting stance.
In a nutshell, Biddle was training Marines to win in weapon to weapon combat (vs. machetes and knives in Central America and bayonets, swords, and knives in the Pacific). Fairbairn and Sykes started out training cops and together during WW2 taught what were essentially "assasination" techniques to be used on an unarmed or unsuspecting opponent.
In a weapon on weapon engagement, particularly in the military, edged weapon context putting your empty hand out to get chopped/cut/smashed up isn't the smartest idea. How useful is the "good guy" if he kills the enemy but loses three or fingers in the process on his other hand? Plus, having the knife to the rear greatly telegraphs the attack.
What typically happens if someone is "knife forward" vs. "knife to the rear", is if the "forward" guy attacks, he aims to put steel on flesh, and the closest flesh is his opponent's empty (lead) arm. Bad guy instantly recoils, either from the pain (and perhaps shock of seeing some fingers disappear) or in an attempt to avoid the incoming cut, then reflexively stabs or slashes. Which because of the position of his arm, is somewhat limited along which angles it can move on. "Knife forward" guy grabs/parries the attack and nails the "knife to the rear" guy in the gut or neck.
With trainers this can get really slap happy, but if both participants take it seriously and envision real knives (and not tactical folders, but something a little larger, like the Marine Raider Bowie, current issue OKC-3S USMC Bayonet, large kitchen knife, Ka-Bar, etc), do you really want to take a cut on your empty hand that will leave that arm crippled, missing fingers, perhaps even a hand?
If the knife has a significant guard (i.e. something at least half an inch, preferably an inch or so) on both top and bottom, and is held in Biddle's "Flat Blade" grip, then the guard will actually protect the hand! (against some attacks) If the knife vertically (or palm up) like many hold it, then the guards do nothing or next to nothing to protect the hand.
Dan
