Flatlander said:
And which drills are those? Would you run us through your groundwork knife drills?
Kinda hard to put drills into words, especially when we might have different language regarding what we are doing...
But, for starters:
Everything starts with a takedown, and that has to be a takedown that doesn't get you needing stiches. My preference is to enter into a 2 on 1, either side of the arm. Lock the wrist down and control the shoulder of the weapon arm.
From there you got to take the guy down, without loosing control of the weapon arm.
If you achieve that the hardest part is over. Depending on what you did to toss him he may already have lost the weapon, but don't count on that...
Now you need to either completely imobolise the arm in a way that you can still attack, or attack the arm. Wrist locks, chicken wings, keylocks.... not likely straight arm bars or bicep splices, but it all depends on what you did to take the guy down.
If you want to look at when someone pulls a knife on you when you are already on the ground, that's a different issue.
If he is in a dominate position, you are already loosing, and if he has a weapon and you are already loosing... well, it's just not gonna be your day is it?
If you are winning, the guys is in trouble, chances of him being able to pull out a concealed knife (and likely have to open it up) smoothly and without you (the guy punching him in the face) knowing about it is not that good.
But give it a try, get a training blade, have your partner conceal it, choose a starting position and go. Once he starts going for it get control of that arm and don't let him use it, get it away.
Or, do it wear you know he has a knife, stick it in his belt or pocket and don't let him get it. He tries too.
Simple drills, and if you don't have a good knowledge of grappling they won't be of any good, that has to be there first.