As a boy in the late 1940s, I was taken to all the New York Giants football games in the dreary, drafty old Polo Grounds. Then as now the Giants were pretty bad, but at least there was one great player to watch each Sunday—No. 45, Emlen Tunnell, the fleet, sure-handed safety, a perennial Pro Bowler, who once held the team records for interceptions, punt returns, and the yardage gained on them.

But Tunnell had another distinction: He was, to use the then-preferred term, the Giants’ only Negro player, one of perhaps a dozen...

As a boy in the late 1940s, I was taken to all the New York Giants football games in the dreary, drafty old Polo Grounds. Then as now the Giants were pretty bad, but at least there was one great player to watch each Sunday—No. 45, Emlen Tunnell, the fleet, sure-handed safety, a perennial Pro Bowler, who once held the team records for interceptions, punt returns, and the yardage gained on them.

But Tunnell had another distinction: He was, to use the then-preferred term, the Giants’ only Negro player, one of perhaps a dozen among the 500 men on the rosters of the National Football League’s 10 teams. Seven decades later, the multibillion-dollar extravaganza that is today’s NFL has 32 teams and nearly 1,700 players. About 70% of them are black and dominate in nearly all positions except quarterback, offensive lineman and kicker.

The origin story of this sports revolution is told in “The Forgotten First: Kenny Washington, Woody Strode, Marion Motley, Bill Willis, and the Breaking of the NFL Color Barrier” by Keyshawn Johnson and Bob Glauber. Football fans know Mr. Johnson as the wide receiver for the New York Jets who famously demanded “Just give me the damn ball!” as a rookie in the late 1990s. His collaborator is an award-winning sportswriter and author.

Bill Willis (60) and Marion Motley (36), lined up for the Cleveland Browns, ca. early 1950s.

Photo: Bettmann Archive

It’s not a pretty story, but in the end a positive one. In its harum-scarum early days in the 1920s, the NFL was a mix of here-today-gone-tomorrow teams based in the industrial Midwest, among them the Milwaukee Badgers, Columbus Panhandles and Decatur Staleys. The celebrated Native American athlete Jim Thorpe played for the Canton Bulldogs, and there was a smattering of black players. Paul Robeson, later the renowned singer, actor and communist sympathizer, played end for the Akron Pros and the Badgers.

But in 1932, George Preston Marshall, a proudly racist laundry mogul, founded football’s Boston Braves, later renamed the Redskins. His inclination and his strategy was to obliterate any black presence in the NFL. As the authors point out, there never was a formal agreement to ban blacks from the league, but there plainly was a gentleman’s agreement (if the other club owners who accommodated Marshall merit the honorific). At the end of the 1933 season, the last two black players in the league—Joe Lillard of the Chicago Cardinals and Ray Kemp of the Pittsburgh Pirates (later the Steelers)—were simply not signed for the next season. And no black hand touched a football in the NFL for the next 13 years.

Enter the unlikely heroes of the tale. One was William Claire “Halley” Harding, the outspoken sports editor of the Los Angeles Tribune, a black-owned newspaper. The other, Paul Brown, was white. He was already a legendary Ohio football coach—first of a high-school team in Massillon, then of the Ohio State and wartime Great Lakes Navy teams—when he co-founded, in 1944, his namesake Cleveland Browns of the new All-America Football Conference, an upstart competitor of the NFL. In 1946, when the Cleveland Rams of the NFL moved to L.A. to play at the publicly owned Coliseum, Harding pressured city officials to deny the stadium to the team unless it signed some black players. Brown, back in Cleveland, was determined to sign two black players he’d coached at Ohio State to his new AAFC team, which was also debuting that year.

Bowing to public opinion, the Rams recruited the versatile back Kenny Washington, who had starred at UCLA and in minor-league pro teams in California, and Woody Strode, a speedy receiver, who was a mix of American black and Blackfeet Indian. Almost simultaneously, the Browns signed Marion Motley, a fearsome fullback, and Bill Willis, an innovative defensive lineman.

The gates were thrown open, but Washington, who was considered the greatest college player ever in California, only limped through them, his knees hobbled from playing in minor-league games while waiting for his NFL chance. Strode’s brief run with the Rams turned out to be a prelude to a long career as a professional wrestler and Hollywood actor (most notably in Stanley Kubrick’s “Spartacus” and John Ford’s “Sergeant Rutledge”). Motley and Willis starred for Paul Brown as his team won an unprecedented five straight pro championships in the All-America Conference and the NFL (after the leagues merged for the 1950 season).

All four of the “First” paid a price. Under the pileups, opposing players punched and kicked them or stepped on their hands. “Alligator bait” and “black bastard” were some of the milder imprecations shouted at them. Down south and elsewhere, hotels turned them away and restaurants denied them service. Occasionally, teams refused to play a game unless the black players were left home. But their teammates and coaches had their backs, and slowly, inevitably, the ranks of black players grew in the league. George Preston Marshall, who had once vowed “We’ll start signing Negroes when the Harlem Globetrotters start signing whites,” was the last holdout. Fifteen years after the color bar was breached, the Kennedy administration muscled Marshall when his Redskins, now in D.C., wanted to move into what became Robert F. Kennedy Stadium, which was built on federal land.

“The Forgotten First” is crisply written and mercifully free of racial cant or sermonizing. Nearly all the major figures in the book have ascended beyond the Hall of Fame to their rightful place in football heaven. So the authors tracked down the children and in some cases the grandchildren of their protagonists to enrich their narrative with family lore. And their reanimation of pro football in the late 1940s and early ’50s—the glory days not only of Marion Motley but of Otto Graham, Bob Waterfield, Gene “Choo Choo” Roberts, Frankie Albert and the rest—is a treat for older fans.

In these fraught days of Black Lives Matter protests and “race-normed” concussion settlements, the NFL is still a field of nightmares. In a recent Netflix documentary, Colin Kaepernick—the quarterback banished for taking a knee during the national anthem—likened playing for the league to “slavery.” Still, “The Forgotten First” is an encouraging American saga of racial prejudice overcome—belatedly but beyond the dreams of those who fought so long to achieve it.

Mr. Kosner is the former editor of Newsweek, New York magazine, Esquire and the New York Daily News.