TOKYO — Japanese tennis star Naomi Osaka is under online attack in her birthplace after speaking out about racial injustice and encouraging people to join a Black Lives Matter march.

Hundreds of people turned out here in the Japanese capital and in the western city of Osaka over the weekend to express support for the movement and to protest racial injustice in the United States — as well as racism in Japan.

The protesters also took aim at Japanese police for allegedly targeting foreigners, after a Kurdish man claimed to have been stopped by police for no reason and shoved to the ground.

The protests have reopened a debate about racism in Japan — and provoked a backlash from right-wing nationalists.

Many people hoped that the rise of Osaka — a two-time Grand Slam winner and former world No. 1 who was born to a Japanese mother and a Haitian father — would encourage Japanese society to be more accepting of people known as “hafu,” or half-Japanese.

Osaka, 22, has deep roots in the United States. She moved to New York with her family when she was 3 and has lived and trained in South Florida for most of her life. She said last year that she was giving up her U.S. citizenship to represent Japan in the Tokyo Olympics, because Japan’s Nationality Act stipulates that those who hold dual citizenship must choose one before their 22nd birthday.

But for some nationalists, acceptance of Osaka seems grudging at best — or conditional on her keeping her mouth shut on political issues.

The tennis champion began speaking out against racial injustice in the United States on Twitter last week, before encouraging people in Japan to join a march in support of Black Lives Matter in the city of Osaka on Sunday.

Her comments sparked a flood of angry responses. Some people argued that the protest could spark a rise in coronavirus infections, and others asserted that racism was not a problem in Japan, or even that the demonstrations were organized by left-wing activists with an agenda.

“Naomi Osaka does not seem to be the pride of Japan,” one person tweeted. “This is my own personal view after all, but I now recognize her as a terrorist. In the future I do not want her to get involved in tennis, a sport played by gentlemen.”

Osaka was undaunted, however, reminding her followers how two Japanese comedians were forced to apologize last year after saying she was “too sunburned” and “needed some bleach.

“I hate when random people say athletes shouldn’t get involved with politics and just entertain,” she also tweeted. “Firstly, this is a human rights issue. Secondly, what gives you more right to speak than me? By that logic if you work at Ikea you are only allowed to talk about the ‘GRÖNLID’?”

Many did rally to her support and denounced the attacks on her.

“Never shut your mouth up and we are always with you,” tweeted Kentaro Iwata, a leading infectious-disease expert. “No to racism of any kind.”

Baye McNeil, an African American author living in Japan, said it was refreshing to see Osaka using her platform and financial security to speak out, but disappointing to see the level of opposition her comments generated.

“That makes me respect her even more,” he said. “She must have known that [her comments would generate a backlash], and I am sure her PR people and publicists were aware of that, but she is telling them ‘I am going to do what I want to do.’ I like that.”

Koichi Nakano, dean and political science professor at Sophia University in Tokyo, welcomed the debate about racism but said the episode revealed the persistence of very conservative attitudes.

“It’s encouraging that quite a number of young people are willing to speak up on the issue, but the bigotry and desire for domination that are still around are also worrisome and disappointing at the same time,” he said.

Activists say police routinely target foreigners in Japan for random checks — although seldom white Westerners — and inflate or massage crime statistics ascribed to immigrants to exaggerate the threat and justify their actions, with domestic media all too willing to play along.

Protesters marching through Tokyo’s central Shibuya district were incensed after video emerged last month of police manhandling a 33-year-old Turkish man of Kurdish origin in the capital after pulling his car over.

The man’s attorney, Yasuaki Nara, said his client has filed a criminal complaint against the police for causing him neck and back injuries while forcing him to the ground.

Police declined to comment on the case, but a police official told the Mainichi newspaper that the man had been speeding and had refused to present his driver’s license and that police restrained him only because traffic was heavy and the situation was dangerous.

On social media, supporters of the police argued that they used reasonable force and that there was no evidence of discrimination. They claimed that the issue is being exploited by activists.

Japan acceded to the International Convention on the Elimination of All Forms of Racial Discrimination in 1995 and says it is “making every effort to eliminate all forms of discrimination.”

Nobuyuki Suzuki, head of the minor nationalist National Party of Japan, tweeted that it was illegal for foreigners to be engaged in political activities.

“We cannot allow activities against Japan’s national interest,” he wrote. “We should send the foreigners who were attending the demonstrations in Shibuya out of the country.”

Japan’s constitution guarantees freedom of expression for foreigners in Japan, but under certain limits — American Ronald McLean’s visa was not renewed in the 1970s after he participated in protests over the Vietnam War, a decision upheld by the Supreme Court.

In South Korea, meanwhile, K-pop band BTS, one of the most popular music acts in the world, donated $1 million to Black Lives Matter last week, according to its label, Big Hit Entertainment. The band’s ARMY fan collective quickly followed up with a separate donation drive, raising an additional $1 million by late Sunday.

Akiko Kashiwagi in Tokyo and Min Joo Kim in Seoul contributed to this report.