Re: The shoulder grab - where does this come from
Dan beat me to it. I've not actually been stabbed or attacked with a knife in "real life", but was shown what can happen if someone grabs either kata-dori or mune-dori with one hand, and pulls you onto the other hand with is augmented by a long sharp bit of steel but which was held out of view during the initial grab.
The sensei in question had us enter to the outside of the grabbing arm with a tenkan - stretching the grabbing arm across our back, and immediately turning back toward attacker with the arm that had been grabbed by the attacker sweeping upwards to join the attacking wrist in an ikkyo...(with the attacker having a bit of a balance issue, following his arm around) - followed by rather forcefully smashing the attacker to the mat and separating his elbow. after all - he DID attack with a knife...
So - say attacker has knife in R hand. grabs your R shoulder with his L hand.
You go beside him to his L, and pivot around to your L, which should lead him to follow you around, raising his R hand to stab (tsuki) as he comes around - you turn back, and with your R hand at his forearm/elbow execute ikkyo, use L hand on his elbow for control and grip his wrist with R hand, and finish the ikkyo to the floor. Pin elbow to ground with L hand, lift his wrist too hyperextend his elbow, and relieve him of the edged weapon. stand quickly and watch for his friends. Don't leave the weapon on the floor for him to collect with his other hand, or for his friends to collect..
Haven't had to do it for real, but it went pretty well in the dojo (without the finishing snap, of course)...