A knife attack has always been the biggest problem in a fight.
knife attacks by definition, are always surprise attacks. Logically, if the person standing next to the attacker knew he had a knife, he wouldn't be near him. Furthermore, most times, knife attacks begin from the back or side, not straight on. This means simply, that if someone is fighting off a knife attack, he's already injured.
Also, depending on how the attacker holds the knife, changes the exact angle of the attack. In addition, to add even more to this very difficult situation, the attacker could be slashing- a forceful and fast sweeping motion, or stabbing- forcing the knife directly into the body. Both are extremely dangerous, and in full speed, look exactly the same.
Because knife attacks are so complicated, the solution must be relatively simple. Don't get used to thinking about the exact angle, it's dangerous. In reality, if your thinking about the angle of the attack, your already stabbed.
Keep it as simple as possible- think attack! Thinking defense, forces a person to come up with numerous variations of blocking from every thinkable position. Not only is it unrealistic, but also extremely dangerous to attempt in reality. When thinking only of attack, the angle makes little difference. No matter where he's attacking, your attacking back.
Keeping it realistic would be drilling the knife fighting principles in through hard and aggressive training; attack the hand with the knife, and control the hand with the knife. Keep it simple.
ICCS Head instructor.