New Study: Courts Recognizing Stress Effects In Excessive Force Litigation

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A new study clearly documents a “significant and important” trend in federal courts to consider the physiological and psychological impact of stress on officer performance in cases alleging excessive force and inadequate training.

“This finding,” says Dr. Bill Lewinski, executive director of the Force Science Institute, “is very encouraging to those of us who have fought for years to get the science of human factors to be part of the legal analysis in cases that challenge officers’ actions in life-threatening situations.

“Hopefully, this trend will only deepen as more judges and juries come to understand the true dynamics of decision-making in tense, uncertain, and rapidly evolving events like officer-involved shootings and other major applications of force.”

The study, the first of its kind, was conducted by Dr. Darrell Ross, a criminology professor, department head, and director of the Center of Applied Social Sciences at Valdosta State University in Georgia.

In a 23-page report in the journal Law Enforcement Executive Forum, Ross offers a valuable compendium of federal district and appellate decisions in cases involving such issues as furtive movements, mistaken perceptions about weapons, vehicles used to attack officers, and other common deadly force controversies.

He also provides specific recommendations for administrators, trainers, and investigators on how best to position their agencies for courtroom victories in cases where human factors may be pivotal.


Drawing on databases maintained by Westlaw and Americans for Effective Law Enforcement (AELE), Ross analyzed 1,000 randomly selected cases published by federal courts from 1989 to 2012, involving police use of deadly force and allegations of constitutional violations under section 1983 of the federal Civil Rights Act.

This pool represents roughly 20% of the decisions written in such cases, he points out. He did not gather unpublished decisions, state-court rulings, complaints that were dropped by plaintiffs, or suits that were settled out of court.

Nearly 90% of the cases he analyzed arose from traffic stops, disturbance calls, warrant service, or investigations of a suspicious person. Nearly two-thirds of the incidents occurred in low lighting. “In 10%…the officer attempted less-lethal options prior to shooting; in 12%, physical control of the suspect was attempted; and in 86%, the officer used verbal commands prior to firing.” In the end, the officers on average had “less than two seconds” to react to what they perceived as a life threat, and on average they fired five rounds.

Of the suspects fired upon, 96% died, Ross writes. About one-third shot or pointed a weapon at police; 30% used a vehicle to attack (“a sizeable number,” Ross says), others a personal or edged weapon. But in nearly one in five cases, “the suspect did not possess any weapon.”

Ross selected 1989 as a starting point for his research, he explains, because that’s when the landmark decision Graham v. Connor was made by the U.S. Supreme Court, recognizing the reality that officers typically must form perceptions and make split-second decisions under adverse conditions and based upon fragmentary information when confronting potentially deadly threats. Ross, a frequent expert witness in police litigation, did his doctoral dissertation on Graham in 1992, at Michigan State University.

That decision established the “reasonableness” standard for judging officers’ use of force and their “perception” of the circumstances. This, he writes, opened the door for introducing “the science of human factors…into the legal analysis of whether [an] officer used justifiable force.”


Although cops often decry their experiences in court, especially in controversial OISs, Ross confirms that in fact police win federal cases significantly more often than not. Of those he examined, “[t]he police were awarded summary disposition in 78% of the cases,” thereby avoiding the need of a trial.

Of the 22% that did go to trial, “the police prevailed in 82%,” Ross found, with the courts ruling that for the involved officers to have believed they faced immediate or imminent threats was reasonable.

All these case decisions “involved circumstantial and environmental factors, suspect behaviors, and human factors impacting the [accused] officer’s perception and decision-making to fire his or her weapon,” Ross reports. “The collective totality of these variables significantly assisted the court or the jury in finding in favor of the police in a high number of cases.”

In short, he told Force Science News, “officers’ perceptions under the influence of stress have become a significant factor in courts reviewing police decisions about use of force.”


In his Forum report, Ross initially details the stress-related cognitive and physiological phenomena that commonly come into play in high-stress encounters. Well familiar to FSN readers and Force Science Analysis trainees, these include a “myriad” of perceptual alterations, lengthened reaction time, inattentional blindness, “instinctive decision-making,” and diminished accuracy of memory, to name a few. (In explaining these performance factors, he cites the research of, among others, Lewinski; Dr. Alexis Artwohl, a Force Science instructor; and Dr. Audrey Honig, a graduate of the Force Science certification course.)

Then Ross addresses the core of his study: the “identifiable patterns” in court decisions that reflect an understanding of such human performance dynamics. These patterns, in effect, delineate guidelines that can help officers to better understand appropriate use-of-force, aid administrators in revising force policies and training methods, and assist investigators in conducting fair and scientifically informed investigations of force events.


Ross groups the court-decision patterns into four categories, reflecting common focal points of use-of-force litigation. For each, he cites specific court decisions to support his conclusions.

First, “sudden furtive movements” by a suspect, such as abruptly reaching “toward a pocket or waistband area.”

Consistent with research by Lewinski and others, Ross writes, the federal courts have recognized that an officer “frequently operates behind the reactionary curve, which places him or her at a significant disadvantage.” Observing the suspicious movement, mentally processing its threat potential, and formulating a defensive response may take an officer from 0.5 to 0.75 seconds, Ross notes, allowing a determined assailant time to shoot or suddenly attack physically before the officer can react. Thus, defensive action “without full deliberation” becomes urgently necessary.

Courts acknowledge that an officer often “does not have the luxury to ‘wait and see’ what an aggressor may or may not do,” Ross writes. “A significant pattern of case decisions make[s] it clear that an officer may use lethal force based on…the perception that he or she is in immediate danger [because of] the suspect’s aggressive movements and behaviors….

“The courts note that it is not necessary that the [perceived] danger actually existed; it is sufficient that the [officer] resorting to self-defense…reasonably believed in the existence of such a danger.” Courts note that “an officer does not have to wait until a gun is pointed at him before the officer is entitled to take action,” Ross writes.


“Frequently,” Ross reports, “an officer may have to quickly determine whether a subject is holding a weapon or something else.” Occasionally, police have shot people brandishing cell phones, pieces of pipe, or other objects mistaken for firearms.

Here, courts tend to consider how an erroneous perception can be formed under “tense, unpredictable, and fast-paced circumstances,” Ross says. Citing professional papers by Lewinski and Honig, for example, Ross itemizes some of the factors that courts may consider:

“Environmental conditions like lighting, distance, visibility, and reaction time, as well as emotional issues like fear, anxiety, and stress may cause and enhance perceptual distortions. Processing visual cues by the brain takes longer than auditory cues; and motion is perceived before color, and color is processed before shape.

“When an officer is forced to process these factors and others under pressures of time and the belief that his or her life is in immediate danger, a mistake-of-fact shooting may occur.” Contributing to the erroneous perception may be the officer’s “prior experiences, expectations, and contextual cues.”

In accepting the reasonableness of wrong perceptions, courts have ruled that “the Constitution does not require omniscience or absolute certitude to act in self-defense,” Ross finds. Officers “need not be absolutely sure of the nature of the threat or suspect’s intent in order to justify the use of reasonable force.”


“An emerging trend associated with a number of shootings is the suspect using a vehicle as a deadly force instrument against the officer,” Ross writes. In this circumstance, “an officer is extremely vulnerable, and the ability to cognitively process a decision to react and to protect his own or another’s safety can be severely compromised.”

Again, Ross finds, courts have been empathetic with a targeted officer’s desperate need to instantly form a perception of threat and to react accordingly, even though the suspect’s vehicle may ultimately turn or back up as well as continue directly at the officer.

Ross cites nearly two dozen cases in which courts have granted qualified immunity to officers who shot suspects who “used or threatened to use [a vehicle] as a weapon.”


The cases Ross studied acknowledged firearms as deadly weapons, of course, but also accepted tire irons, bats, pipes, bottles, fireplace pokers, axes, golf clubs, hatchets, mechanical tools, edged weapons, police batons, pieces of concrete, and flashlights, “to mention a few,” as having lethal capability as well.

Whatever the deadly instrument, courts are recognizing that in an attack an “officer is at a distinct time disadvantage and behind the perceptual processing and reactionary curve,” Ross writes. “Even if the barrel of a gun is pointed down and away, a quick movement to raise, aim, and fire it…can occur before the officer can react.”

In a “significant” number of incidents, Ross reports, courts have found officers “justified in using preemptive force” because of the time crunch. “In a majority of incidents, the courts opined that the officer is not required to wait and see what a suspect may do, as the officer is a fraction of a second (or more) behind the suspect’s actions and such a disadvantage places the officer in a position of immediate harm, which justifies the use of lethal force.”


Based on his parsing of court decisions, Ross recommends the following:

Policy revision. Administrators should revise use-of-force policies to conform with “the philosophy of Response to Resistance,” which bases force responses on the subject’s actions. Policy should state that the reasonableness of force will be “assessed in conjunction with the officer’s perception [of the threat] at the moment force was used” and “within the totality of circumstances,” as prescribed by the Graham decision.

Language which directs an officer to “use the minimum amount of force or the least intrusive amount should be removed from existing policies.” Every federal court, Ross says, “recognizes this point.”

Training focus. Because excessive force complaints are commonly coupled with claims of failure to train, Ross emphasizes the importance of modernizing training. To meet today’s standards, he writes, training must be realistic, frequent, intense, and “designed to replicate field stressor variables and environmental conditions” and incorporate decision-making and human performance factors.

That means moving beyond stale qualification routines into dynamic scenarios and Simunitions exercises that “help officers understand how to recognize assault cues, cognitively process them, make solid decisions, perform under stress and be able to articulate their decision process.”

He believes that training for field officers and command staff alike should include regular updates on court decisions related to use of force. Sworn personnel “need to be aware of how the courts assess lethal force decision-making in the field” and how they evaluate the impact of human factors in life-threatening circumstances.

In conversation with FSN, Ross pinpointed the need at academy and in-service levels for training related to vehicular attacks on officers, “a subject that hasn’t really been addressed much” despite its significant representation in the cases he examined.

Investigative enhancement. Along with other important training, Ross considers it vital that “[a]dministrators and investigators who are tasked with evaluating an officer’s use of lethal force” have a solid education in human performance factors “associated with survival stress.”

This includes gaining a thorough understanding of such things as cognitive processing, threat and assault cue recognition, perception formation, perceptual alterations under stress, reaction time principles, time-compressed decision-making, and the impact of stress on memory.

As Force Science also teaches in its certification course, he recommends that for best recall OIS interviews should be conducted after involved officers have had one or two sleep cycles and should follow a cognitive interviewing format.


Ross told FSN that he is midway through a new study that may impact law enforcement policy, training, and procedures.

With the cooperation of more than 20 departments, he is exploring the results of proning out resistant subjects during the arrest process. His findings, he believes, will suggest whether so-called positional asphyxia, an alleged fatal consequence of a violent suspect’s breathing being compromised when restrained face-down, is truly a menace or a myth.

Data collection will end in December, Ross says, and he hopes to present preliminary results at the annual ILEETA conference next March. (A more limited study of the subject in Canada by Force Science instructor Dr. Christine Hall has revealed no exceptional link between prone positioning and injuries or deaths.)

Ross is author of the book Civil Liability in Criminal Justice, now in its sixth edition. His full report on his court decision study, titled “Assessing Lethal Force Liability Decisions and Human Factors Research,” includes more than 100 pertinent case citations for ready reference. The article can be accessed by clicking here.

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