Fourteen-year-old Connor Leibel just felt overwhelmed.

He was sitting in a sunny and quiet neighborhood park in suburban Phoenix while his caretaker visited a nearby store. To calm himself, Leibel, who is autistic, started “stimming” with a piece of string—an exercise commonly taught to people with autism to help them cope with stressful environments.

But that’s not what it looked like to Officer David Grossman. Grossman, who the Buckeye Police Department has called a drug-recognition expert, said he thought Leibel was bringing his hands toward his mouth to somehow inhale drugs. After driving by multiple times, Grossman stopped to ask Leibel what he was doing.

“I’m stimming,” Leibel replied, taking a few jerking steps back, footage of the July 19, 2017, incident captured by Grossman’s body cam shows.

Grossman apparently didn’t know what that meant. He told Liebel to stop walking away, while Leibel, confused, told him “it’s a string.” After the teen awkwardly told the officer he didn’t have identification on him, Grossman grabbed his arm and tried to restrain him. In a blur of fast movements that are difficult to distinguish in the footage, the pair hit a tree and fall to the ground.

The camera captures Grossman struggling to pin down the teen, while Leibel, his breaking voice rising in increasing panic, repeatedly screamed “I’m OK, I’m OK, I’m OK,” as the policeman on top of him tells him to “stop moving” and “relax.”

Moments later, when Diane Craglow, Leibel’s caretaker, arrived at the scene, she told the officer that the boy was autistic. As she looked on in horror, Leibel, his voice trembling, asked her, “Am I going to be OK?”

Craglow tried to explain to the heavy-breathing policeman that “he [was] stimming,” to which Grossman replied, “Yeah, I don’t know what that is,” while Leibel continued to struggle beneath him.

After speaking with the caretaker, Grossman began to soften and deescalate the situation. He dropped a pair of handcuffs to the ground, and stood up to release Leibel. But the damage had already been done.

“He pushed me down on the grass and he just hit me on the tree, and he tackled me and then he didn’t stop,” Leibel later told CBS News. “It made me feel sad.”

In a case filed this week in a Phoenix federal court, Leibel’s family is suing the city of Buckeye, Arizona, its police department, and Grossman for punitive damages “on nine counts, including battery, excessive force, negligence, failure to train, and illegal arrest,” Courthouse News reports. They also seek civil penalties, and a corrective injunction that would force the department to better educate its officers on how to interact with people with disabilities.

In court documents cited by Courthouse News, the Leibels claim Grossman had no training in dealing with people with autism, and that he admitted as much while speaking with their son’s caretaker. They also claim that Leibel was “forcibly restrained, slammed against a tree, and pinned to the ground by” the policeman.

“Connor was doing nothing illegal,” the complaint states.

The Buckeye Police Department has insisted that Grossman did nothing wrong. “Within 20 seconds of contact, Connor goes to run from the officer,” Police Chief Larry Hall told West Valley View. “The officer holds on to him and they fall to the ground. There’s no escalation of force at that point.”

In an initial claim filed in January, the Leibels said Grossman had a history of poor conduct within the department, noting a personnel file that said “supervisors have long been ‘concerned that [Grossman’s] situational awareness may not be adequate enough for the rigors of law enforcement.” In a separate incident predating Connor’s, Grossman was documented as having grabbed a suspect at a park, wrestled him to the ground, and “deployed a chemical agent” twice to his face. A department Performance Improvement Plan for Grossman appeared to recognize a problem: “As we have previously discussed, ‘seizing’ a person requires articulation which you could not provide when you performed these actions.... Looking for charges after an arrest is made is unacceptable and unconstitutional.”

According to the court documents, Leibel “suffered cuts, bruises, and scratches to his face, back, and arms from the attack, and a grotesquely swollen ankle, which required surgeries.”

But it’s the emotional damage from the incident, the January claim argues, that is more severe. “A feature of Connor’s condition is that he often relives past grievances over and over, without an appreciation of how far in the past they occurred. Consequently, Connor continues to relive the events of last year in excruciating detail,” the claim states. “He asks if he is going to be hurt again when he sees a police car. In fact, he expresses fear of meeting new adult men in general—something that he never experienced previously. His parents are anguished at the changes they witnessed in Connor.”

According to one of the family’s lawyers, Timothy Scott, the lawsuit was filed to prevent this from happening again. “Officer Grossman detained and injured a child, literally because of the boy’s autistic mannerisms,” Scott told The Daily Beast via email. “Targeting a person based on their disabilities violates basic civil rights and the Americans with Disabilities Act. After this first happened, the family asked for three things: 1) an apology from the officer; 2) that the officer perform community service with the autistic community; and 3) that Buckeye institute a mandatory training program to prevent an incident like this from ever happening again. Sadly, they never even responded to our letters.”

Buckeye PD has repeatedly argued that Grossman’s use of force was justified. Shortly after the event, it cleared him of any wrongdoing. In a September news release, the department wrote that Leibel was “moving his hand to his face in a manner consistent with inhaling, and then [Grossman] observed the teenager’s body react accordingly after that movement,” and that Grossman “lawfully detained the teenager, causing both of them to fall to the ground,” according to NBC affiliate 12News.

And in any case, the department said its “officers receive training on a variety of situations, including interactions with people who have disabilities.”

“I hope the family sees that we will learn from this incident and we are human and things are constantly evolving and changing—absolutely—and it’s almost impossible to know and understand every single little piece of every single disorder,” Det. Tamela Skaggs told CBS News.

As the January claim notes, misperceptions like Grossman’s are illegal under the Americans with Disabilities Act (ADA). According to the ADA, the claim says, an arrest is considered wrongful even if an officer “misperceive[s] the effects of [a victim’s] disability as criminal activity.”

“We can do a better job in dealing with people with disabilities in the community,” Chief Hall told West Valley View, describing to the paper how the department enhanced its training procedures in the weeks after the Leibel incident and became the lead on a grant to provide officers training on dealing with individuals in crisis. “It’s our responsibility, as holders of the grant, to make sure other agencies benefit from this and the training. We understand how important that is. There’s a narrative out there that we don’t care about people with disabilities. That’s simply not true. It’s not accurate.”

The Buckeye Police Department did not immediately respond to a request for comment.

But other actions the department has taken regarding disabilities have caused controversy in Buckeye. In November, it implemented a voluntary registry program for individuals with autism, Alzheimer’s, bipolar disorder, panic disorders, and schizophrenia. Each diagnosis corresponded to a different colored wristband, which the department asked registry members to wear for self-identification.

Leibel’s mother, Danielle, was angered by the proposal. “I think it’s disgusting that you have to label someone with a disability with a special mark so they don’t have to live in fear from being hurt by police,” she told ABC15.

Will Gaona, a representative for the ACLU, agreed. “People with disabilities shouldn’t have to broadcast their diagnosis to the world, just because police officers have insufficient training.” he told ABC15. “A better solution would be to have special wristbands for officers who’ve found to be engaged in excessive use of force, so the public knows who they’re dealing with.”