You asked a question about fighting with a knife and everyone says "run away!" Strange.
We all know the best idea is to extract yourself from the situation, but if you cannot...
Knife fighting is extremely dangerous but not necessarily difficult to become effective at against your "average street thug". The idea is to make it extremely dangerous for the other guy.
However if you have NO CHOICE and HAD it defend yourself with a knife nothing will beat good training.
Check out the US Army Field Manual mentioned above it has some very good basic information.
While I do NOT in any way consider myself an expert (regardless of my High Speed Low Drag nickname
) I completed a basic training course in the service and then progressed to advance H2H.
Nothing much scares me more than the thought of facing off against a skilled knife fighter, or even a thug for that matter.
I have however, defended myself a couple of times with a knife. I have been cut twice and stabbed in the back once (nicked a lung and a nasty scar). Nothing I would ever want to repeat.
After training with the service I pursued training with a martial arts school, as I previously could not carry a gun back home, (another country). The "kung fu" school taught similar techiques as the military and focused completely on effectiveness. They were very very good.
So get a good sturdy knife within the legal requirements of your state (over 3" here in Colorado is considered a weapon and if concealed is a crime without CCW) Obviously if possible fixed blade over folder, longer over shorter. Try and find a good school.....
oh and don't forget to stab more than slash.