McKINNEY, Tex. — No lives were lost. The incident played out at a suburban pool party, not an urban neighborhood struggling with crime and drugs.

But perhaps it was that suburban setting that helped make the images so powerful and disturbing. Now a video of a police officer pointing a gun at teenagers in bathing suits and shoving a young black girl’s face into the ground has become the latest flash point for relations between the police and minorities.

The cellphone video taken at the community pool in Craig Ranch, a racially diverse subdivision north of Dallas, has sparked another debate over race and police tactics, with activists calling for the officer to be fired and others arguing that the blame should fall at least in part on the teenagers.

The video appears to show the officer, David Eric Casebolt, briefly waving his handgun at young partygoers who approached him as he attempted to subdue the teenage girl on Friday. The officer ultimately immobilized the girl by putting her facedown on the ground and placing his knees on her back.

Chief Greg Conley of the McKinney Police Department said the video prompted an internal affairs investigation and Officer Casebolt, a patrol supervisor, had been placed on administrative leave.

One adult man was arrested on charges of interfering with the duties of a police officer and evading arrest, Chief Conley said. The 14-year-old girl who was immobilized by Officer Casebolt was “temporarily detained,” but ultimately released to her parents, he said. Benét Embry, the host of an Internet-radio talk show, lives in the neighborhood and saw the party grow out of control. Mr. Embry, who is black, said that as many as 130 young people attended the party.

He said that some of them scaled the pool’s fence after being turned away from the entrance by a security guard, who eventually called the police.

“As an African-American male, of course I had a concern seeing a 14-year-old African-American female in a swimsuit on the ground,” Mr. Embry said in a phone interview on Monday. “Of course I had concerns when I saw the officer pulling a gun. That’s when I started thanking God that nobody got hurt. But I don’t believe that the officer was coming out to pick on black kids.”

McKinney, a northern suburb of Dallas with around 150,000 people, is a fast-growing, mostly middle-class enclave with deep racial and economic divisions. In 2009, according to an article in The Atlantic, the city settled a lawsuit in which it was accused of hindering the construction of affordable housing in the western part of the city, which is more white and more affluent.

The pool party took place on the west side, in a neighborhood that residents said is usually marked by friendly relations among black, white, Hispanic and Asian residents. In a statement, the Police Department said officers arrived at the pool at around 7:15 p.m. on Friday, responding to a call about a “disturbance involving multiple juveniles at the location, who do not live in the area or have permission to be there, refusing to leave.

The department, the statement added, received “several additional calls related to this incident advising that juveniles were now actively fighting.”

McKinney’s mayor, Brian Loughmiller, said in a statement that he was “disturbed and concerned by the incident.”

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Interactive Graphic: The Race Gap in America’s Police Departments

Outside of Police Headquarters on Monday, activists said the youths had been subjected to racial bias, and demanded that Officer Casebolt be fired. Dominique Alexander, the president of the Next Generation Action Network, a civil-rights group, said that it was an “illusion” that kids had been jumping the fence. “They had every right to be there,” he said.

After the video spread quickly online, criticism poured in from around the country. The A.C.L.U. of Texas said that it while it did not have all the facts about the party, “what we do know is that the police response, as seen on the video, appears to be a textbook case of overuse of force.”

In a video posted to YouTube on Sunday, two days after the party, an African-American teenager named Tatiana said her family was hosting a cookout for friends when a woman insulted them, prompting a 14-year-old family friend to respond. Tatiana said a white woman then told her: “you need to go back to where you’re from” and to “go back to your Section 8 home.”

Tatiana said she replied “excuse me,” –and then another white woman hit her in the face and “both women attacked” her.

Mr. Embry, the neighbor who saw the party, said that he did not see a fight involving blacks and whites.

He described a party that began with a D.J. playing music in a nearby park, but that soon grew out of control as the security guard began turning away teenagers who were not allowed in the pool area.

The video of the police response shows Officer Casebolt using profanity and shouting at teenagers as he and others officers attempt to round up some of them, and shoo others away from a chaotic scene. He appears to grab the girl in frustration when she does not leave the area.

In an interview with KDFW-TV, the girl restrained identified herself as Dajerria Becton. She told the television station that she was invited to the party and had not been involved in a fight.

Brandon Brooks, 15, who shot the video, told a TV station that Officer Casebolt did not confront him, one of the few white teenagers at the party.

“I was one of the only white people in the area when that was happening,” Mr. Brooks told the station. “You can see in part of the video where he tells us to sit down, and he kind of like skips over me and tells all my African-American friends to go sit down.”