She Took a Knee in College. She’ll Do the Same as a Pro.

It almost didn’t feel like a choice to Kaiya McCullough. She was 19, a U.C.L.A. sophomore with hopes of becoming a professional women’s soccer player, when she first decided to take a knee during the national anthem.

“I remember being so compelled — it was an energy all of a sudden,” McCullough said. “I need to kneel. I need to do this.”

So, long before George Floyd’s killing, long before she was drafted into the National Women’s Soccer League by the Washington Spirit earlier this year and long before she started training for the start of her pandemic-shortened rookie season, McCullough knew she would take a knee as a professional athlete, too.

She also knew her decision came with real risks, and that the last N.W.S.L. player to do it, Megan Rapinoe in 2016, had faced a hailstorm of criticism. But McCullough, who is black, felt secure in her choices. “I was willing to accept whatever consequences came with it,” she said.

On Saturday, when McCullough’s Washington Spirit faces the Chicago Red Stars in her first professional game, she is not likely to be alone. The debate around kneeling and the role athletes can play in conversations about social justice has shifted quickly. When the N.W.S.L. becomes the first professional contact sports league in the United States to return to play this weekend, kicking off a monthlong tournament in Utah, McCullough, now 22, and others expect several players to take a knee.

“That might rub some fans the wrong way, but I honestly think that if you see it as being a flag issue and not a human issue at this point, I just don’t really care,” said Lynn Williams, a North Carolina Courage forward who will play in the tournament’s opening game, against the Portland Thorns.

Colin Kaepernick’s decision to take a knee during the national anthem before N.F.L. games became a cultural flash point in 2016. But Kaepernick’s silent action, intended to raise awareness of racism and police brutality, has surged and spread around the world in the wake of mass protests of Floyd’s killing while in police custody. Soccer players in France and Germany now kneel after goals, and entire teams in England’s Premier League have taken a knee together at the start of each match.

But with most sports in the United States on pause during the coronavirus outbreak, the question of how American athletes would handle the renewed Black Lives Matter protests remained unanswered.

After Rapinoe knelt in solidarity with Kaepernick during the anthem in 2016, becoming the first white player to do so, she faced immediate backlash, including from McCullough’s new team, the Spirit.

When Rapinoe’s team faced the Spirit soon after she began kneeling, Washington unexpectedly played the national anthem while the teams were in the locker room. At the time, the team said it did not want Rapinoe to “hijack” the anthem.

But McCullough said the Spirit, which now has a different majority owner, has said she will face no repercussions. “The universe was looking out for me, getting drafted to where I did,” she said. “I’ve felt nothing but overwhelming support.” She made her intention to kneel clear in interviews earlier this month.

For McCullough, the seeds of her protest were sown during a childhood in conservative Orange County, Calif., where she grew up with a white mother and black father, playing a sport that remains overwhelmingly white in the United States.

She said she was first seized by the realization that the country’s promise of equality was not true for all Americans when she was in high school, during protests after the killing of Michael Brown in Ferguson, Mo. McCullough decided she could no longer stand for the Pledge of Allegiance at school.

“I didn’t think of it as activism then,” she said. “I just thought, ‘I can’t stand and say this.’”

It angered many people at her school. Teachers sometimes gave her no choice but to stand, she said, and a boy she had considered a friend once erupted at her, telling her to “go back to Africa.”

At U.C.L.A., McCullough found a different culture. When she decided to kneel, her team found ways to show solidarity. They first took a knee as a group, and then those who wanted to stand during the anthem did. Sometimes, teammates knelt with her. Always, at least one put a hand on her shoulder.

It wasn’t always easy. During away games, there were sometimes catcalls, and there was a deluge of racist comments after TMZ picked up the story. McCullough was often nervous, she said, “but I did it anyway.” She does not expect to be alone on Saturday, or to escape notice.

The N.W.S.L.’s opening game, featuring the defending champion Courage against the Thorns, will air on CBS — the first time a league game has been shown on broadcast television. (McCullough and the Spirit will take on the Chicago Red Stars later that day, on CBS’s All Access streaming service.)

The N.W.S.L. Players Association said it planned to use Saturday’s national platform to show support for the Black Lives Matter movement. It is unclear how many players plan to kneel, but there are other demonstrations planned, a player representative said. The N.W.S.L. said it had been “collaborating” with the union “to assist a player-led initiative in support of the Black Lives Matter movement and the goal of eliminating racism and injustice.”

The efforts have been led by black players like Williams, Sydney Leroux and Crystal Dunn — voices that have not always been elevated in a sport where many of the biggest stars are white. (Dunn said recently that she felt she could not join the kneeling protest by Rapinoe, the team’s most popular player, in 2016 because she was “scared that it’s going to look different if a black girl on the team kneels.”)

The opportunity presented by the shift in support has been exhilarating, but also exhausting, for black players who have also been expected to train in the midst of the country’s turmoil. After Floyd’s death, McCullough said, it was sometimes hard to get out of bed, much less to play soccer.

Now she mostly feels excited. To her, this moment feels different.

“I’ve had so many more conversations in the last month than in the three years that I was kneeling,” she said.