Jaylen Brown is 23. Sterling Brown is 25. LeBron James, one of the older players in the league, is only 35. All three, like so many of their N.B.A. compatriots, are part of an emboldened generation of Black athletes, a vanguard challenging America’s norms in numbers never seen before.

At the very same time, the Republican National Convention represented and embraced an entirely different vision — one nostalgic for the past, wary of change and angry for an entirely different reason. Sports personalities from an era when player protests were rarer figured prominently. Lou Holtz, the renowned 83-year-old college football coach who last led a team 16 years ago, proclaimed steadfast devotion to President Trump and spoke triumphantly of a mythical America where anyone can succeed by just working hard enough.

Herschel Walker and Jack Brewer, both Black former N.F.L. players out of the league for well over a decade, struck the same tone, hailing Trump as a heaven-sent crusader against racism and a proponent of social justice, ignoring a reality that says the opposite.

Two visions. Two Americas.

2020 vs. years gone by.

The N.B.A. is hardly alone. Walkouts rippled this week through the W.N.B.A., and through predominantly white sports like professional tennis and soccer. Games were postponed because of protesting players in conservative, tradition-bound Major League Baseball. At first the National Hockey League continued with its playoff schedule, before bending to pressure and taking a pause.

This was the logical next step in the fervent activism inspired this year by the killing of George Floyd. As the nation grappled with 401 years of racial trauma, it searched for ways to break apart systemic injustice and violence against Black Americans.

Players as prominent as Kyrie Irving of the Brooklyn Nets declared that holding a season now, resuming amid the pandemic, was a mistake and a distraction — and called for athletes to stay home and work within their communities for change.

But the N.B.A. and the W.N.B.A got back to work. The players chose to use nationally televised games as a platform for their grievances. They draped their courts and jerseys with slogans and calls for change. They knelt during the national anthem.