When Can You Threaten Deadly Force as a Defensive Tactic?

This question is in the news because of the St. Louis controversy (see, e.g., here and here); but I thought I'd discuss it more broadly, because the answer is surprisingly unsettled.

[1.] To begin with, recall that, as a general matter, you can lawfully use deadly force to prevent death, serious bodily injury, kidnapping, or rape, if you reasonably fear such harm. In about half the states, you can use it to prevent robbery (forcible theft from your person). And in some states, you can use it to prevent arson (even arson that doesn't threaten death or serious bodily injury, such as arson of some outbuilding) or burglary of your home or possibly even your business or workplace.

But you generally can't use it if all you reasonably fear is mere trespass on your open land (e.g., your lawn) or minor vandalism or even a physical battery short of serious bodily injury. You can use nondeadly force to stop such lesser harms, but not deadly force. For more details, see this post, but let's rely on this (admittedly oversimplified rule) for now.

[2.] If you can lawfully use deadly force, then you can lawfully threaten deadly force, e.g., by pointing a gun at someone or saying "get out of here, or I'll shoot you." So if, for instance, you tell a trespasser that they're trespassing (or even threaten nondeadly force to tell them to stop trespassing), and they turn on you and credibly threaten to kill you (the St. Louis man's story), then you can generally use deadly force to protect against that threat.

[3.] If you can't lawfully use any force (for instance, against people who aren't trespassing but are merely peacefully protesting on a public sidewalk, even in front of your house), then you can't lawfully threaten deadly force, either.

[4.] But say that protesters are trespassing, so you're allowed to use nondeadly force to eject them: Perhaps they are on your driveway or your lawn. I don't know the Missouri law on whether residents of a gated community where the roads and sidewalks are private may use nondeadly force to eject trespassers, so let's turn to the clearer case where they are on your own property, or are threatening to damage your property in a fairly minor way (as opposed to, say, through arson or some other especially harmful action).

Can you threaten deadly force even when you can't lawfully use it? (Assume they are merely trespassing, and you don't reasonably believe them to be threatening something much worse.) On that, states disagree. The LaFave & Scott Criminal Law treatise tells us that "merely to threaten death or serious bodily harm, without any intention to carry out the threat, is not to use deadly force, so that one may be justified in pointing a gun at his attacker when he would not be justified pulling the trigger." Likewise, Black's Law Dictionary defines "nondeadly force" to include a "threat of deadly force, such as displaying a knife." (See this post on the Siwatu-Salama Ra case from Michigan.) That seems to be the majority view.

But it's not the view everywhere, and in particular not in Missouri, see State v. Kendrick (Mo. Ct. App. 2018):

Kendrick was accused of "knowingly exhibit[ing], in the presence of one or more persons a .45 Caliber pistol, a weapon readily capable of lethal use, in an angry or threatening manner." "The Missouri Supreme Court has held that unlawful use of a weapon by exhibiting it in an angry or threatening manner constitutes 'deadly force' for the purpose of … justification defenses." State v. Cummings (Mo. Ct. App. 2017) (citing State v. Parkhurst (Mo. 1992)). Thus, the … statutory elements that must have been established by substantial evidence in order for Kendrick to inject the issue of self-defense in this case are [in relevant part -EV]:

[a] that Kendrick … reasonably believed physical force was necessary to defend himself from what he reasonably believed to be the use or imminent use of unlawful force of another (section 563.031.1);

[b] that Kendrick reasonably believed deadly force—that is "'physical force which is used with the purpose of causing or which a person knows to create a substantial risk of causing death or serious physical injury'"—was necessary to protect himself against death, serious physical injury, or {"any felony involving the use or threat of physical force or violence against any individual, including but not limited to murder, robbery, burglary, arson, kidnapping, assault, and any forcible sexual offense"}, or was necessary to use against a person who had unlawfully entered, attempted entry, or remained after unlawful entry into his residence (section 563.031.2(2), (3)); ….

The evidence, viewed in the light most favorable to Kendrick, established that Williams was unarmed, raised his voice, and pushed Kendrick three times before Kendrick retrieved a handgun. Thus, Kendrick "'introduced a deadly instrument into what had been, at most, a simple battery and significantly raised the level of violence.'" "'[D]eadly force [including, in Missouri, the threat of deadly force -EV] cannot be used to repel a simple assault and battery.'" Instead, "[d]eadly force is only justifiable when the defendant reasonably believes that such deadly force is necessary to protect himself from death, serious physical injury, or any forcible felony." Here, the evidence established, at most, that Williams committed a simple assault and battery against Kendrick. There was no evidence that Kendrick reasonably believed deadly force was necessary to protect himself against death, serious physical injury, or any forcible felony.