But there is more to it than that, and it extends farther than the N.F.L., to the National Basketball Association and beyond. The politicization of sport may have as much to do with our previous president as it does with Donald Trump. A lot of professional athletes were drawn to President Obama, a black man, basketball junkie and ESPN habitué with a degree of cool they recognized — and they were moved for the first time to direct political engagement. They raised money and campaigned with him.

Politics and social action can have an addictive quality. The basketball superstar LeBron James, for one, perhaps the nation’s most popular athlete and one of its most thoughtful, seems hooked. In 2016, he spent time on the campaign trail with Hillary Clinton.

Social media has also played a role. Many black athletes in the past were not willing to have their social or political views mediated through a world of sportswriters who were almost entirely white. That’s no longer a concern. Few groups in America have been better served by social media than professional athletes. They never much trusted writers to carry their message out to the public, and now they don’t have to. LeBron James communicates directly with 38.6 million people who follow him on Twitter. Stephen Curry of the Golden State Warriors, another prominent Trump critic, speaks to 10.5 million followers.

The current generation of coaches is also a factor. They are less authoritarian and more attuned to their players’ hearts and lives. Some of the most prominent among them are also the most worldly and, almost certainly, the most liberal in their politics, and they understand that encounters with police are the great leveler for the multimillionaire black athletes they coach.

“Our players clearly understand what it is to be marginalized,” Pete Carroll, the coach of the N.F.L.’s Seattle Seahawks, told CNN’s Anderson Cooper on Tuesday. “And they know that when they’re not football players and they’re off the field in their everyday lives, and they know that when they’re with their children and they have to prepare their children to act properly and be safe because of the things that they’re up against.”

Gregg Popovich, the coach of the N.B.A.’s San Antonio Spurs, lit into President Trump at a news conference on the first day of training camp this week and then spoke more generally about race relations. “Why do we have to talk about it?” he said. “Well, because it’s uncomfortable and there has to be an uncomfortable element in the discourse for anything to change. Whether it’s the L.G.B.T. movement or women’s suffrage, it doesn’t matter. People have to be made to feel uncomfortable, and especially white people, because we’re comfortable.”

Since when does a guy coaching a pro basketball team call out white privilege and talk about L.G.B.T. rights and women’s suffrage? Now. He talks about it now. For anyone who has followed sports — or has written about it, as I have, over the course of several decades — it is shocking, if not disorienting.