What do I do if someone pulls a knife on me?

Honestly? You ain’t gonna have time to react at all so it is pretty much a moot point. If you actually SEE the knife and have opportunity to react, that knife is being utilized as a threat display in hope that you will back down, or the individual is too far gone on drugs, drink, or mental illness to care about the consequences of his actions. In either case you should immediately RUN. If you are with other people, the guy will be completely focused on *you* to the point of literal tunnel vision. Do not worry about them. When they berate and mock you afterwards, say “He had a knife” and that should be that.
I have witnessed dozens of knife attacks in person, and at least a thousand more on video. The guy waving the knife around generally is not the problem. He *wants* you to see the knife and either leave him alone or comply with his demands. Nope, the guy you need to worry about is the one who pulls a blade the moment he feels he is losing the fight. This usually happens in the clinch, or immediately after you take him to the ground. There is no hesitation… he just stabs you between three and seven times before pushing you off him and running away.
Most people do not even feel the knife… they think he was just punching them… but then they feel wetness, their legs go weak, they become dizzy, they stagger and slur like a drunk, they become cold, their vision blurs, and then they usually die. Most of the bleeding is internal, and if it is a dimly lit venue with loud music, most onlookers will not even realize what happened, especially if he is wearing dark clothing and manages to sit down before passing out… everyone will think he is sleeping.
The other way I’ve seen knives used is in an ambush. There is no “fight,” more like an assassination. There is an argument, someone gets shoved or slapped and storms off… an hour later he comes back, or hides in a bathroom stall, or waits in the shadows outside. The guy never sees it coming… several rapid stabs in the back and he vanishes.
So, if you SEE the knife, it is your lucky day. You can apologize, beg, yell “HE HAS A KNIFE” and fling an ashtray in his face before sprinting to the pool table and hucking billiard balls in his direction like a monkey flinging poo, then snap off the tip of a cue and use the sharp tip as a spear. If there is no ashtray or pool table, fling a glass full of ice in his face, followed by beer bottles. Get distance between yourself and the knife. Wrap your weaker arm in a jacket or towel, or grab a trashcan lid, but RETREAT rather than attack. They used to teach using a chair or stool to trap and disarm a knifer, but unless you are security staff who has trained in this tactic you have no business attempting it because it is unlikely to work. Getting away from the threat is your primary goal. Escape, not engagement.
If you really want to overpower a knifer, you should have thought ahead and brought a gun.
C. R. Jahn, author of FTW Self Defense

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