Having studied dozens of knife fights/attacks caught on camera one thing that stands clear to me is that trying to control the knife hand of the antagonist does not work. I have yet to see a "disarm" as so
widely taught in modern day martial arts schools, actually work. What usually happens is that the person with the knife presses his attack alternating high and low strikes. Something always gets through and the person stabbed starts a spiral into oblivion.
Trying to control the knife hand is instinctual. But its bad juju... Consequently, in training we should focus on rewiring our reaction. If you are close enough to grapple with the knife hand, you are close enough to impart a debilitating injury to the neck/eyes/groin. Turn off the brain of your antagonist and the knife/hammer/gun/thunderbolt-- becomes moot.
If you have a training partner, start working in literally slow motion (try not to stop as you start hitting targets). In the very beginning, just have your partner stand there with a training knife in hand as you pick targets to start the process of turning off his brain. Your partner should be mimicking spinal reactions to injuries. As you grow more comfortable, you can incorporate a strike to the knife hand as you then attack your targets to induce serial injury and unconsciousness. The attack to the knife hand, if executed properly, is a strike with your forearm/ulna bone to his forearm and will cause your antagonist to drop the knife. The next step would be to have your knife wielding partner instigate an attack and execute your counterattack accordingly. Through it all, work slowly and deliberately to make each strike hit the target you are trying to hit.