When I was younger I used to think myself quite the bad ass and I hung out with a far different social class than my own economic situation and upbrining would naturally place me in. I witnessed a knife fight once. Thank god no one died but it appeared as though its random slashing with not very much finesse. Blade length prevents more coordination of specific moves and counters and the dirty nature by which you would come to a knife fight prevents any sort of real skill. Most of these knife fighting experts are mostly nonsense, if you find yourself in a knife fight you can do one thing, run. Barring this try to make some form of guard for your off wrist and absorb blows with this while dealing damage with your knife hand. And thirdly stab as well as slash. I guarantee 90 percent of people in knife fights slash wildly the other ten percent are people trained to kill.

In other words knife fights have no real defense beside being quicker and disabling your opponent first.