This will be tough since the attacker will most likely try to get free, so you must hang on as tightly as you can. Affect the attacker's hand. As soon as you can, slam the attacker's hand against a hard surface. If necessary, you can even try to break the attacker's wrist or hand. The more you struggle, the more damage you can do to your assailant. If you are being attacked with a knife, your first goal is to survive the attack. You can't use force to stop an attack, only an object that could cause serious injury or death if used properly. If you can disable your attacker by hitting them in the head/neck area, doing enough damage for them to drop their knife, then this is a good idea. However, keep in mind that once they realize you are disabled they may try to finish you off. So if possible, fight back. The next thing you need to know is how to disarm your attacker. This depends on how the knife was carried during the attack. If the attacker had the knife in their hand, you should be able to grab it easily and disarming them this way will be simple. However, if they were hiding the knife under their clothing then you won't be able to find it until after they are restrained. At this point, you can still disarm them but it will take some time.