Facing a Knife...

Even a skilled fighter will have problems dealing with weapons.

A 12 year old youth with a knife is  every bit as dangerous as a full grown assailant.

DON'T under estimate anyone who is ARMED.

Firstly NO sudden movements. Give nothing  that will panic the attacker and cause them to cut you.

Remember they are desperate and HYPED up - and any sudden move on your part could be FATAL.

In the opening seconds be compliant, raise your hands up and say something like "OK, you can have my money, I'm not going to mess with you!" Anything along those lines to relax them somewhat.

DON'T say things like "got a knife to feel brave, eh?".

This kind of statement only serve to 'wind' them up and they may cut you out of anger.Whatever you decide to do next you must to quickly and sharply, control the knife arm and go in whole heartily to VITAL points. Get it
done quickly.

Once you have deflected the blade DON'T  overlook kneeing or grabbing testicles, butting the face, elbowing the throat and hitting the knife anywhere else.

Also close up as a distraction, in the opening  few seconds, spitting in there face will instantly make them 'cringe' - then go for the counter.