Caveats:
This diagram does not represent a particular jurisdiction, but should be fairly accurate for most jurisdictions. Most of the weapon systems/techniques should be within two or three levels of force. What this means is that some places might have Arrest/Control techniques being less force than pepper spray. Don't try to do math with it: you don't get four applications of pepper spray equaling one application of firearms in terms of liability. This is not the law, but a model for thinking about how different levels of force and liability interact.

Firearms & Knives: Firearms refers to all handguns, rifles, or shotguns. For the purposes of describing force and liability there is no difference or disparity between them. Additionally a knife is as much of a threat as a firearm. It is very likely that people who are shot, stabbed, or cut will die or be permanently injured. The threat posed by an attacker with one of these weapons allows for a lethal force response. This explains why the police might shoot an attacker with a knife: because his capacity for causing injury or death is on the same level.

Impact Weapons Impact weapons are things like police batons, and baseball bats. This is kind of a grey area, because an attacker swinging a bat is not the same thing a police officer swinging a nightstick. The police by virtue of training can use a baton in a less lethal manner to subdue combative subjects, where as the attacker cannot reasonably be expected to have the same training or intent. The diagram reflects this by splitting the difference between High and Moderate risk of injury or death.

Striking Techniques Punching, kicking, throwing, and similar techniques have a moderate risk of injury or death. This risk takes into account that getting while getting hit can cause you to be; knocked down, cause head injuries, or break bones the general expectation is not permanent injury or death.

Arrest/Control Techniques This is meant to reflect coercive, pain compliance techniques. The likelihood of permanent injury or death is less than striking people, but still significant. Any time you a grappling with a person who is resisting there is a chance for injury.

Tasers & Pepper Spray These compliance tools have a low expectation of causing permanent injury. These tools are poorly understood by the general public. They are used frequently by law enforcement to subdue threatening or non-compliant subjects because they pose less risk of harm for officers and the subject than any other physical means. There is some controversy in the media about people dying after being sprayed or tasered at some point in the encounter, but I have not seen anything where a taser or pepper spray was the cause of death. Hundreds of thousands of police officers have been tasered and sprayed in the course of training with no lasting effects.

Verbal Commands Issuing orders to deter or achieve compliance poses no risk of injury nor has any liability. Like presence, the implied threat of force may be enough to deter or gain compliance.

Presence Uniformed police officers can deter or gain compliance by implied threat of arrest. In it's simplest form we could say that presence is simply physical intimidation, the implied threat of force may be enough to deter or gain compliance. There is no risk of physical injury or liability associated with presence.

Take away points:

• While private citizens are not bound law enforcement policy, actions taken in self-defense that are within the guidelines for the police are prudent, and more defensible.
• The amount of inherent 'force' a tool or technique has is based upon the potential for serious injury.
• Liability increases with the amount of force, so solve your problems with as little force as is necessary.