The decals, with messages such as “Stop Hate” and “Black Lives Matter,” are part of the league’s efforts to show solidarity with players who have protested against racism and police brutality.The N.F.L. will allow players to display messages of social justice on their helmets and will stencil the slogans “It Takes All of Us” and “End Racism” on the end zones at every field as part of an effort to show solidarity with the protest movements against racism and police brutality, league officials said.As the league prepares for the first game of the season on Thursday, an N.F.L. spokesman said that players would be allowed to choose a decal with one of six messages to place on the back of their helmets: “End Racism,” “Stop Hate,” “It Takes All of Us,” “Black Lives Matter,” “Inspire Change” and “Say Their Stories.”Last season, the N.F.L. also allowed players to display messages such as “Stop Hate” and “Black Lives Matter” on their helmets, as well as the names of Black people, such as George Floyd, Breonna Taylor, Trayvon Martin and Ahmaud Arbery, whose deaths set off widespread protests.The efforts represent a continued shift for the league, which in the past had been criticized as slow to support, or hostile to, players who had demonstrated against racism and police violence.About 70 percent of active players on the league’s rosters are Black and league officials have been trying to show unity with those who have demonstrated against injustice, particularly after the murder of Mr. Floyd in May 2020.“It’s an opportunity to highlight messages that are important to the league, players and personnel and our communities,” Brian McCarthy, the N.F.L. spokesman, said on Saturday. “We’ve seen tremendous work done by our players to make an impact, and we can increase that through the high-visibility platform that the N.F.L. provides.”The efforts have been shadowed by the specter of Colin Kaepernick, the onetime quarterback for the San Francisco 49ers, who in 2016 began kneeling during the national anthem to protest police brutality against African Americans.Mr. Kaepernick and others who knelt during the anthem set off an intense backlash by some fans and conservatives, including former President Donald J. Trump, who accused them of being unpatriotic.Mr. Kaepernick left the 49ers in 2017 and has not been signed by any team since. In 2019, he reached a multimillion-dollar settlement over his claim that the league had spurned him because of his protests.That year, the N.F.L. also began a program called Inspire Change that directs donations to groups focused on police-community relations, criminal justice reform, education and economic advancement. Last year, the N.F.L. said it was nearly tripling the size of its commitment to the program, pledging to spend up to $250 million over 10 years.Amid the protests set off by Mr. Floyd’s death, Roger Goodell, the N.F.L. commissioner, released a videotaped message last year condemning racism and the systemic oppression of Black people. His message came one day after a group of players had released their own video calling on the league to send just such a message and to “admit wrong in silencing our players from peacefully protesting.”“We, the National Football League, admit we were wrong for not listening to N.F.L. players earlier and encourage all to speak out and peacefully protest,” Mr. Goodell said in his message. “We, the National Football League, believe Black lives matter.”Last year, the league also honored Mr. Floyd, Ms. Taylor, Mr. Arbery and others through an initiative called “Say Their Stories.”Mr. McCarthy said on Saturday that there had been no change in the league’s stance about kneeling during the anthem. Players are “strongly encouraged” to stand for the anthem, he said, but the N.F.L. does not plan to take action against those who choose instead to kneel, raise a fist or remain in the locker room.“We’ve never fined one player” for kneeling, he said. “No player has ever been disciplined.”The end-zone slogans, he said, will be featured during every game, except for those that honor specific causes. For example, during a “Salute to Service” game honoring the military, “End Racism” will be replaced with “Salute to Service” in one end zone, and “It Takes All of Us” will remain on the other end zone, he said.“Lift Every Voice and Sing,” known as the Black national anthem, which the N.F.L. played before games in the opening week of last year’s season, will once again be played before the start of this season’s first game between the Dallas Cowboys and the Tampa Bay Buccaneers on Thursday, Mr. McCarthy said. The song will also be played at the Pro Bowl, the Super Bowl and the N.F.L. draft, he said.George Atallah, a spokesman for the players’ union, the N.F.L. Players Association, said on Saturday, “Our membership continues to not only care about these issues, but have been putting in the time and effort to effectuate change in their communities.”