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Deadly force, as defined by the United States Armed Forces, is the force which a person uses, causing—or that a person knows, or should know, would create a substantial risk of causing—death or serious bodily harm. In most jurisdictions, the use of deadly force is justified only under conditions of extreme necessity as a last resort, when all lesser means have failed or cannot reasonably be employed.
Firearms, bladed weapons, explosives, and vehicles are among those weapons the use of which is considered deadly force. The use of non-weapons in an aggressive manner, such as a baseball bat or tire iron, may also be considered deadly force.
"Use of deadly force" is often granted to police forces when the person or persons in question are believed to be an immediate danger to people around them. For example, an armed man in a shopping mall shooting at civilians without regard to the safety of anyone around him, and refusing or being unwilling to negotiate, would warrant usage of deadly force, as a means to prevent further danger to the community. The use of deadly force is also authorized when a person poses a significant threat to a law enforcement officer, usually when the officer is at risk of serious bodily injury or death. In the United States this is governed by Tennessee v. Garner, which said that "deadly force...may not be used unless necessary to prevent the escape and the officer has probable cause to believe that the suspect poses a significant threat of death or serious physical injury to the officer or others." This case established the Fleeing felon rule exception to the use of deadly force. Under this exception, if a police officer establishes probable cause that an individual escaping poses a serious threat of death or significant harm to the officer or others, the officer can use deadly force. In Australia, it has recently been proposed that police officers should have this power when a person might in the future pose a threat to others (see Australian Anti-Terrorism Act 2005).
Most police agencies establish a use of force continuum and list deadly force as a force of last resort. With this model, agencies try to control excessive use of force.
In general, all armed bodies, be they the police or military or some offshoot thereof, have the ability to issue authorization for the usage of such force.
In the United States, a civilian may legally use deadly force when it is considered justifiable homicide, that is to say when the civilian feels that their own life, the lives of their family, or those around them are in legitimate and imminent danger. However, self-defense resulting in usage of deadly force by a civilian or civilians against an individual or individuals is often subject to examination by a court if it is unclear whether it was necessary at the point of the offense, and whether any further action on the part of the law needs to be taken.
Legal opinions 
Use of deadly force in relation to motor vehicles: In Scott v. Harris, No. 05-1631 (April 30, 2007). , the U.S. Supreme Court held that a police officer’s attempt to terminate a dangerous high-speed car chase that threatens the lives of innocent bystanders does not violate the Fourth Amendment, even when it places the fleeing motorist at risk of serious injury or death. In the Harris case, Officer Scott applied his police car's push bumper to the rear of the suspect's vehicle, causing the suspect vehicle to lose control and crash, resulting in the fleeing suspect being paralyzed waist down.
Traditionally, intentional contact between vehicles has been characterized as unlawful deadly force, though some U.S. federal appellate cases have mitigated this precedent. In Adams v. St. Lucie County Sheriff’s Department, 998 F.2d 923 (11th Cir. 1993). , the Seventh Circuit Court of Appeals ruled that although fatalities may result from intentional collisions between automobiles such fatalities are infrequent, and therefore unlawful deadly force should not be presumed to be the level of force applied in such incidents; however, the Adams case was subsequently called into question by Harris v Coweta County, 406 F.3d 1307 (11th Cir. 2005). , which in turn was reversed by the U.S. Supreme Court in the Scott v. Harris case discussed above; the extent to which Adams can continue to be relied on is uncertain. In the Adams case, the officer rammed the suspect's vehicle.
In Donovan v. City of Milwaukee, 17 F.3d 944 (7th Cir. 1994). , the Seventh Circuit Court of Appeals recognized this principle but added that collisions between automobiles and motorcycles frequently lead to the death of the motorcyclist, and therefore a presumption that unlawful deadly force was used in such intentional collisions is more appropriate. In the Donovan case, the suspect lost control of his motorcycle and became airborne, crashing into the officer's vehicle, which was parked as part of an intercepting roadblock.
||This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. (January 2010)|
- AFI 31-207 Arming and Use of Force by Air Force Personnel
See also 
- Fleeing felon rule
- Licence to kill (concept)
- Non-lethal force
- Rules of engagement
- Stand your ground law