TLDR: Using a knife for self-defense can put a character on some shaky ground. The best tactic, legally speaking, is to inflict an injury that allows for a retreat when one is otherwise not possible.

It’s a lot of fun to choose knives for characters. I played the part of armorer for a vigilante detective character not long ago, and I enjoyed the hell out of it. The blades in that instance (I recommended two for the character) were to be used for last-ditch self-defense. I stopped short, however, of detailing what self-defense with a knife can mean in a legal sense.

Maybe this matters to a story and maybe it doesn’t. But if you’re going to assign a character a knife, don’t disregard how easy it is for a knife-wielding character to cross the line from self-defense to murder.

Disparity of Force

It seems simple enough at first. A character is attacked and uses a knife for defense. The character keeps slashing away until the bad guy is bleeding out the last seconds of life onto the floor, or something to that extent. Open and shut. Case closed, right?

Not quite. Here’s the rule of thumb:

Self-defense laws, typically set at the state level, don’t necessarily consider intent (“I was only defending myself”) or the level of injury (“I stabbed him, but I didn’t mean to kill him”). They consider disparity of force.

This disparity exists when the person threatened is outmatched by one or more people. An elderly woman in a wheelchair versus six young men. A small woman versus a large man. A couple on a date versus a gang of werewolf biker women (I don’t know, bear with me, people). Even a person with a gun versus someone with a knife, if the distance between them is 21 feet or less (link is NSFW).

In general terms, that disparity can be legally evened out with the application of deadly force. For example, Granny can use the hidden handgun beneath the knitting project on her lap to shoot the lowlifes trying to beat and rob her.

However, even dear old Gran must stop pulling the trigger once the threat to her is gone. If the lowlifes turn and run away, she must stop shooting. The disparity of force no longer exists because the threat is hustling it down the street. She must act reasonably, and in some cases may even have a duty to render aid, otherwise she’s committing murder instead of self-defense. State laws shade that reasonableness differently, but the general idea is the same.

Knives and Disparity of Force

Now apply that same concept to knives. If Granny is attacked and pulls a knife, then proceeds to slash the throats of those lowlifes (she’s pretty bad ass, possibly a member of a werewolf biker gang), the disparity of force is no longer present to justify her violence. Granny overpowered the lowlifes. Despite her original intent of self-defense, her actions could mean she committed murder. In fact, the lowlifes might even be justified in using deadly force against her, depending on the laws of the setting.

This is why self-defense with knives is such shaky ground. In order for that blade to make those injuries, you must have some sort of physical advantage. That’s why the best tactic is to inflict an injury that allows a retreat when one is otherwise not possible. If one of the lowlifes wraps a hand around Granny’s wrist, and the only way she can break free is to stab the bastard in the arm, then the use of that knife is probably justifiable.

None of that means the scenario is over, though.

Knife Injuries can be Ambiguous (NSFW Photos)

Even the goriest bits of pop culture don’t quite capture the brutality of a knife attack. This post on Lee Lofland’s blog, however, does. If you can stand them, you won’t forget the photos there.

While they do reveal plenty about human anatomy, those graphic wounds don’t tell whether they were inflicted on the right or wrong side of the law. It’s this ambiguity that the court system would have to unravel.

Don’t think a prosecutor wouldn’t exploit those knife wounds to play on a jury’s sympathies. After all, the person inflicting those wounds must’ve had a physical advantage, right? And instead of retreating, he or she stuck around to kill or maim someone in one the most brutal ways possible. This is how otherwise good people go to prison.

Like I said before, these legal considerations might not matter to a work of fiction. Readers probably aren’t interested in legalese. But for procedurals and legal thrillers, this is good stuff to consider. (In that case, I recommend this book.)

Turning Heroes into Murderers

The next time you read a novel, watch a movie or zone out for a TV show that features a fight scene, pay attention to when a bad guy is “finished off” by the protagonist. You might be surprised how often the supposed hero is actually a murderer. You might not be surprised, however, at how easily this point is skimmed over.

Of course, this kind of subtlety is absent in video games. Sorry, Mortal Kombat fighters, but you’re all due for a stint in prison.

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The Writer’s Guide to Weapons: A Practical Reference for Using Firearms and Knives in Fiction (Writer’s Digest Books) comes with everything but the ammo. Pick up a print or digital copy from these fine retailers:

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