On Monday, NBA player Kyle Korver dropped an essay at The Players’ Tribune that, in the sports world at least, seemed to stop time. It felt like everyone in the basketball universe actually put down their social-media accounts, stopped texting one another, and took 10 minutes to read and ponder the truth bombs Korver was throwing down.

His piece is called “Privileged” and it’s remarkable. Korver, who has played in the NBA for 15 seasons, speaks about the experience of being white in the NBA and having, well, the privilege to not have to deal with the institutional racism that affects his teammates and their families. He writes:

What I’m realizing is, no matter how passionately I commit to being an ally, and no matter how unwavering my support is for NBA and WNBA players of color.… I’m still in this conversation from the privileged perspective of opting in to it. Which of course means that on the flip side, I could just as easily opt out of it. Every day, I’m given that choice—I’m granted that privilege—based on the color of my skin.

He also writes about the obligation that white people have to back up their black teammates, neighbors, or co-workers—and to do so with humility:

We have to support leaders who see racial justice as fundamental—as something that’s at the heart of nearly every major issue in our country today. And I have to support policies that do the same I have to do my best to recognize when to get out of the way—in order to amplify the voices of marginalized groups that so often get lost. But maybe more than anything? I know that, as a white man, I have to hold my fellow white men accountable.

Korver goes on to say that this isn’t about navel-gazing. It’s about struggle. “I’ve come to realize that when we talk about solutions to systemic racism—police reform, workplace diversity, affirmative action, better access to healthcare, even reparations? It’s not about guilt. It’s about responsibility.” His words echo Ibram X. Kendi, who has written often that “it is not enough to be non-racist. One must be anti-racist.”

It’s a remarkable essay, and it’s also a challenge. Korver isn’t the first white athlete to publicly come out in support of black struggle. Lou Moore’s book We Will Win The Day: The Civil Rights Movement, the Black Athlete, and the Quest for Equality spends a chapter detailing white athletes who back in the day in the 1940s and ’50s stood with their black teammates as they challenged Jim Crow and other forms of discrimination. Peter Norman, famously, stood alongside John Carlos and Tommie Smith on the medal stand at the 1968 Olympics.

More recently, in 2016, soccer star Megan Rapinoe knelt in solidarity with Colin Kaepernick, saying:

Being a gay American, I know what it means to look at the flag and not have it protect all of your liberties. It was something small that I could do and something that I plan to keep doing in the future and hopefully spark some meaningful conversation around it. It’s important to have white people stand in support of people of color on this. We don’t need to be the leading voice, of course, but standing in support of them is something that’s really powerful.… It’s the least I can do. Keep the conversation going.

White women athletes stood—and kneeled—alongside their black teammates in protest after the police killings of Alton Sterling and Philando Castile. But in the Black Lives Matter era, there have been precious few white male athletes at the collegiate or professional level who have had much to say about racism, privilege, and their role in the struggle.

Korver’s essay changes that. It has gone viral and has been praised by LeBron James and Golden State Warriors coach Steve Kerr. NFL player Chris Long, who is from Charlottesville and has had his own political awakening in the aftermath of 2017’s white-supremacist violence in his city, praised the piece on social media.

Korver’s last statement, while specifically directed at white players in the NBA, could just as easily apply to white NFL or MLB athletes:

People of color, they built this league. They’ve grown this league. People of color have made this league into what it is today. And I guess I just wanted to say that if you can’t find it in your heart to support them—now? And I mean actively support them. If the best that you can do for their cause is to passively “tolerate” it? If that’s the standard we’re going to hold ourselves to—to blend in, and opt out? Well, that’s not good enough. It’s not even close.

The challenge to all white athletes has now been posed—which side will you be on moving forward? Just being “non-racist” isn’t going to cut it.