Blake was tackled and handcuffed by police in a case of mistaken identity in front of the Grand Hyatt Hotel during the 2015 U.S. Open. (Kevin Hagen/for The Washington Post)

It took James Blake 22 years of training to reach No. 4 in the world and advance to the U.S. Open quarterfinals, among the highlights of a distinguished tennis career. But it took just 12 minutes to turn him into an accidental activist.

The life-changing episode would be difficult to believe had it not been captured on a time-stamped hotel surveillance tape that still shocks two years later.

Then 35 and recently retired from the pro tour, Blake was standing in front of New York’s Grand Hyatt at noon on a sun-streaked Wednesday waiting for a car to take him to the 2015 U.S. Open for an appearance when a burly, bald man in street clothes rushed toward him. Mistaking him for a high school wrestling buddy he hadn’t seen in 20 years, Blake was more bemused than alarmed as the man lunged, wondering how his friend had tracked him down.

Without a word, the man tackled him, twisting Blake’s left arm and grabbing him by the neck as he threw him face-first on the concrete, thrust a knee in his back and slapped on handcuffs.

“I’m cooperating, whatever you say,” Blake said, letting his body go limp as images of news accounts of the nightmarish consequences of resisting arrest filled his mind. “I’m complying 100 percent, whatever you say.”

Blake: “Had circumstances been different, it could have escalated rapidly to a violent end.” (Kevin Hagen/for The Washington Post)

The plainclothes New York police officer never showed a badge or identified himself as he turned Blake over and stood him up, handcuffed amid one of the city’s busiest crossroads, a few hundred yards from Grand Central Station.

“This is a mistake. This is an absolute mistake,” Blake said as five other undercover officers converged.

His first thought — after the police realized their mistake and uncuffed him — was to brush it off. He was an athlete; he was tough, he told himself. His wife demanded otherwise. “What if this had happened to me — or someone else you cared about,” she pleaded after he phoned to tell her what happened.

So, after consulting with his agent, Blake told his story publicly that afternoon. That night, the two met with a lawyer to discuss how to proceed.

The response they crafted turned an all-too familiar, disturbing fact pattern into a positive.

Rejecting the idea of a lawsuit despite incontrovertible evidence of excessive force, they decided to create something that would help New Yorkers in similar situations who lacked Blake’s notoriety and means for challenging police mistreatment. The upshot is a legal fellowship in Blake’s name, funded by the city, that will provide a lawyer within the Civilian Complaint Review Board dedicated to helping citizens with a grievance negotiate the legal maze and hurdles that dissuade many from going forward. (New York’s CCRB is an independent agency that investigates allegations of police misconduct and abuse).

“I wanted to do something that was going to make a difference,” Blake, grandson of a police officer, said in an interview last week. “More than 50 percent of the cases last year where there wasn’t a fatality but someone sustained minor injuries from the police department weren’t seen to completion. A lot of people don’t have the means to continue. They just give up hope.”

Under the settlement, which was signed in June, the first lawyer to fill the James Blake CCRB Fellowship will start work in January, according to Zachary Carter, Corporation Counsel of the City of New York.

“This is one of those rare situations where you can say it’s a ‘win-win’ and really mean it,” said Carter, the city’s chief legal officer, who brokered the agreement with Blake and his lawyer, Kevin H. Marino. “If complainants don’t understand the system — don’t understand that it’s all about developing evidence to support their claims — no one is served by that.”

Blake agreed not to sue the city, but James Frascatore, the police officer who manhandled him, faces a public disciplinary trial on charges of using excessive force. Blake has been waiting nearly two years to testify in the proceedings, which have been postponed multiple times.

Meanwhile, he has written a book, “Ways of Grace: Stories of Activism, Adversity, and How Sports Can Bring Us Together,” that recounts the events of Sept. 9, 2015, and explores how athletes across sports have raised their voices on issues of social justice for decades.

“My incident gave me one of the chapter titles in the book — Accidental Activist — and it sort of made me one of those, too,” Blake said. “If not for this incident, there’s a good chance I wouldn’t have been speaking so passionately or been so informed about police brutality.”

Writing the book proved cathartic and illuminating, like going back to school for a course he wanted to study, said Blake, who left Harvard after his sophomore year to turn pro.

“I wanted to show examples of athletes who have lived a life that’s bigger than their sport,” Blake said. “Athletes aren’t just people you see on the TV screen for two or three hours. They have families. They have social consciences. They have bigger goals and dreams than just their sport.”

Blake highlights former Minnesota Vikings punter Chris Kluwe, who has spoken in favor of same-sex marriage. He discusses Peter Norman, the Australian sprinter who stood in solidarity with Tommie Smith and John Carlos during their raised-fist protest on the medal stand of the 1968 Olympics and paid a harsh price for it. And he writes about Billie Jean King’s determination to “change the world” by using tennis to advocate for gender equity.

Blake, whose British mother is white and late father was African American, also recounts instances of violence against black Americans by law-enforcement officials that spawned the Black Lives Matter movement. And he explains that before NFL quarterback Colin Kaepernick refused to stand for the national anthem to protest police brutality, the NBA’s Mahmoud Abdul-Rauf had his vacant house burned down after remaining seated in prayer during the national anthem in 1996 because he believed the flag conflicted with his Muslim beliefs.

Said Blake: “For all those people who want to say, ‘Just play sports and shut up,’ there are athletes who say: ‘No, I have a conscience and I’m gonna say what I want to say. If you don’t like it, you don’t have to be a fan of mine. But it’s my right to speak my mind.’ ”

The book’s title, chosen before he’d written the first word, is an homage to the late Arthur Ashe, the tennis champion whose memoir is “Days of Grace.”

“Arthur Ashe was someone who did everything in his power, whether he was on top of the world or in a grave situation, to help others,” Blake said. “He didn’t ask, ‘What is this going to do to my popularity? How is this going to enrich me?’ He asked, ‘How can I help others who are less fortunate than I?”

That was Blake’s mind-set after the 2015 encounter with police, according to Marino, his lawyer.

“As we talked this through that night, he was quite aggrieved by what had happened,” Marino said. “It was a jarring event, but he made it very clear from the outset that this was not going to be a case involving the pursuit of financial reward.

“He certainly knew he had been wronged, but he immediately perceived that the real harm that had been done wasn’t so much to him but to the general rule of law. And he saw a parallel to incidents that, at that time, were very much in the public eye. He was simultaneously the victim, in a ‘small-v sense,’ but in a ‘big-V sense,’ a very good stand-in for others who have experienced this.”

Blake, once the country’s top-ranked male tennis player who lives in San Diego with his wife and two daughters, was back in New York last week for events related to the U.S. Open. He also met with Marino to prepare for Frascatore’s trial, now scheduled later this month. During the meeting, they watched the hotel video of the incident one more time.

“Almost daily, I think about what could have happened,” Blake said. “What could have happened if I didn’t think [the officer] was a friend and thought he was someone running at me to hurt me? There’s a good chance I would have put my arms up, or tried to fight back or would have run instinctively.”

Or, Blake wonders, what if his older brother, Thomas, had been with him and come to his defense?

“Had circumstances been different,” Blake said, “it could have escalated rapidly to a violent end.”

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