Just what is the 'Ferguson effect'? It depends on how you view police.

It’s a brief, but telling moment in the video from the McKinney, Texas, pool party gone wrong: When two African-American teenage boys surround an officer kneeling on a bikini-clad girl, the officer, Eric Casebolt, reacts by grabbing his gun and briefly waving it around.

To some Americans, like Fox News’s Sean Hannity, Mr. Casebolt acted appropriately, since he could have been “shanked,” as Mr. Hannity put it. To others, the flash of video shows two teenagers trying to rescue their bikini-wearing friend from an armed maniac. (No one was hurt, but the officer resigned and the teenagers weren’t charged with any crime.)

The moment in the McKinney video highlights a debate over the so-called Ferguson effect. Reflecting 10 months of sporadic, sometimes-violent anti-police protests over the killing of Michael Brown in Ferguson, Mo., and other black men elsewhere, the phenomenon, for some, is that America’s criminal elements are feeling emboldened to question police authority – which in turn has meant a more hands-off approach by officers and a spike in some localized crime rates.

But others say the Ferguson effect more accurately describes a political movement where oppressed black Americans are increasingly standing up for their rights. On Wednesday, a Philadelphia judge ruled that 10 protesters arrested for being unruly at a town-hall meeting on community-police relations were not guilty of any crime, since their admittedly disruptive speech was political in nature and thus protected by the First Amendment.

The debate over police tactics and race in a country where the Constitution makes no mention of a constabulary goes back more than a century, and will probably continue beyond this moment.

Yet some political scientists say the arguments over the Ferguson effect – and whether it has really fueled a murder wave in cities like Baltimore, New York, and Atlanta – also hint at a country searching for a new equilibrium on how policing should look in a country where serious crime, for the vast majority of citizens, continues to become exceedingly rare.

“If we’re talking about a Ferguson effect where it means more people challenging police, more people filing suits against the police, and more people confronting police publicly, I think you are seeing that,” says George Ciccariello-Maher, a political scientist at Drexel University in Philadelphia. “The other dynamic of this so-called Ferguson effect is the notion that when people know their rights, they become dangerous criminals.”

For his part, Mr. Ciccariello-Maher calls the latter idea “utterly absurd.”

But others point to troubling crime trends in cities like Baltimore, which saw 43 homicides in May even as arrests by Baltimore police fell by 57 percent from the previous year. Baltimore is where six officers were indicted for their alleged role in the death of Freddie Gray while he was in police custody.

Meanwhile, murders in New York are up by 20 percent, and St Louis, where the civil unrest began last August, has seen shootings spike by 39 percent and homicides by 25 percent. Police have also had a rough year, with 57 officers killed across the country, compared with 27 last year. Over a greater span of years, it should be noted, the number of slain police officers has stayed fairly constant, and the total number of officers killed in the line of duty has been halved since the mid-1970s.

Still, “the cops I’ve spoken to say it’s different now,” Peter Moskos, a former Baltimore police officer who is now a professor at John Jay College of Criminal Justice, told Time magazine. “Cops are saying, ‘If we’re going to get in trouble for well-intentioned mistakes, then [forget] it, I’m not working.’ ”

Given that the sharp, localized crime spikes have come against the backdrop of highly publicized incidents, “the most plausible explanation of the current surge in lawlessness is the intense agitation against American police departments over the past nine months,” writes Heather MacDonald, the author of “Are Cops Racist?,” in The Wall Street Journal.

Statistically, criminologists say, the numbers mean little, since it’s too soon to extrapolate what’s at the root of some cities’ crime surges. What’s more, the argument is based in part on statistical cherry-picking.

Until a spate of murders in May, for example, Baltimore’s murder rate this year had hewed to historical averages. New York’s spike was compared only with the previous year, when the city saw a historically low murder rate.

Referencing a 30 percent year-to-year murder increase in Atlanta, local police officials said, “There is no clear nexus indicating any specific cause for the increase.”

Nevertheless, such numbers are politically powerful in a country that has seen past upheavals over race and policing. Responses have ranged from President Nixon’s “Southern strategy,” which was largely based on the crime fears of whites, to the emergence of academic discussion about young, black “superpredators” in the 1990s.

“Anytime crime goes up is an opportunity to point fingers at political leaders, so you get The [Washington] Post blaming the mayor, the crime rate going up only in cities with Democratic leadership, and even the ‘Obama crime wave,’ ” says James Alan Fox, a Northeastern University criminologist. “The silver lining to this spike is that, what goes up must come down, which is good news for leaders in Chicago, New York, and Baltimore, since they can then take credit for solving the crime wave that never was.”

But for now, the issue has caused polarization in the broader public, with those who say police need to be left alone to do their jobs in high-crime areas being challenged by those who see the “Black Lives Matter” movement as a new civil rights fight.

“We have seen, since Ferguson, an increase in the number of instances of police use of force captured [on video] and disseminated through news media, and that has led to increased public distrust of police officers and dissatisfaction with police activity,” says Jeffrey Ian Ross, a criminologist at the University of Baltimore.  

That debate blew up with the McKinney video. A Florida school principal, for one, was demoted after posting comments supportive of officer Casebolt’s actions on his Facebook page. 

“Police culture is not just among the police, but throughout society, and that’s where you get references to the police officer in McKinney as a hero,” says Ciccariello-Maher, the political scientist. “When Sean Hannity says that the boys might shank the officer, what he’s saying is that black children are already inmates, because that is the language of prison."

He continues, "The most shocking part of it is that not only are black teenagers more subject to suspicion, scrutiny, and arrests, but for [some Americans], they’re already part of that system, which speaks volumes about this claim that there’s a connection between these incidents and crime.”

Exacerbating the debate is that there’s almost no consensus on exactly why US crime has gone down over the long term.

The effect of so-called broken windows policing, where officers focus on petty crimes to thwart major crimes, has been “modest” on the crime rate, studies show, even as it’s alienated some minority neighborhoods. Also, states that have begun to winnow down their prison populations from record highs in the late 2000s have seen few indications of an ensuing crime problem on the streets.

Marijuana decriminalization; increased government aid to the poor, including affordable health care; and a boom in gun ownership are among the reasons cited for the US crime rate being halved since 1992. Indeed, the decline in the crime rate has been so strong and prolonged that many sociologists are still baffled by the fact that it continued even as unemployment and wage stagnation took hold during the Great Recession.

But to many police officials, the unquestioned authority of police, even given incidents where individual officers appear to have violated the civil rights of citizens, is the crucial thing keeping both officers and citizens safe, especially in areas with lots of known crime activity. That those areas are more often than not African-American neighborhoods is irrelevant, they say, since all Americans deserve to live in relatively crime-free areas.

“While those with agendas continue to disregard evidence, rules of law, and fact, in lieu of the self serving, emotional and fictitious claims, the Ferguson Effect continues to grow,” Steve Loomis, union head for the Cleveland Police Department, which has been the subject of civil rights probes by the US Justice Department and has dealt with two controversial police shootings recently, said in a statement. “The unfortunate and unintended result has been that those that need us the most will be made to suffer from increasing lawlessness of an emboldened criminal element.”

To be sure, for many police officers, widespread criticism of police behavior and tactics has been until the past year a largely a foreign concept. As recently as 2013, Gallup found that Americans think cops are more trustworthy than priests.

Statistics also show that police officers, historically, rarely pay for mistakes made in the field, in part because they have special protections extended to them by the US Supreme Court. Such exceptions allow police to make even deadly errors in situations where they have to make split-second, life-and-death decisions.

But given changing public perceptions and high-definition video, officers’ actions have begun to receive greater scrutiny. In the past year, officers have been arrested in Charlotte, N.C.; North Charleston, S.C., and Baltimore in cases where unarmed black men died at the hands of cops. On Thursday, a judge in Ohio suggested that the officers involved in the killing of 12-year-old Tamir Rice last year should be prosecuted.

In light of such institutional critiques of police behavior, “police union chiefs who talk about the Ferguson effect ought to examine the way they contribute to this so-called Ferguson effect,” says Clarissa Hayward, a political scientist at Washington University in St. Louis. “For police [leaders] to have the mentality of, ‘We’re going to support every action by every police officer,’ that confuses the public, and makes it seem like they’re supporting these clearly racially biased incidents that we’re seeing with our own eyes.”

“I think the police leaders who want to fix [the Ferguson effect] problem really need to do some self-questioning and ask what role they’re really playing, and what they can do to regain trust after communities of color have seen so many of these incidents,” she adds.