By the time Art Shell became the first Black head coach in modern NFL history, there had already been 18 Black head coaches in the NBA and four Black baseball managers.

In this Jan, 13, 1990, file photo, Art Shell, head coach for the Los Angeles Raiders, watches from the sidelines during their AFC divisional playoff NFL football game against the Cincinnati Bengal in Los Angeles. AP file photo

In 1989, two months after his induction into the Pro Football Hall of Fame as a player, Shell took over the head coaching job of the Los Angeles Raiders. He was the NFL’s first Black head coach since the league’s early days in the 1920s, when Fritz Pollard was player-coach for the Hammond (Ind.) Pros. (At the time, the upstart NFL was mostly limited to major and not-so-major Midwestern cities.)

When Shell was fired six years later in 1995, there were two Black head coaches remaining in the NFL.

Last year, Brian Flores of the Miami Dolphins has filed an explosive class-action lawsuit against the NFL and its teams, claiming discrimination when it comes to hiring and retention of Black coaches. The NFL and the teams named in the suit have denied the allegations.

Shell’s hiring marked a significant — albeit belated — milestone for the NFL. Few could have imagined that more than three decades later, there would still be just one Black coach.

Raiders owner Al Davis hired Shell to replace Mike Shanahan — who, coincidentally, had succeeded a coach named Tom Flores, the league’s first Latino head coach. Brian Flores, the son of Honduran parents, is Black and Latino, and when the Dolphins hired him, he became the fourth Latino coach in NFL history. His dismissal leaves just one Latino coach, Washington’s Ron Rivera.

“It is a historic event. I understand the significance of it,” Shell said when he was hired. “I’m proud of it, but I’m also a Raider. I don’t believe the color of my skin entered into this decision.”

If it was a historic development for the NFL, it was hardly groundbreaking when it came to professional sports. A generation earlier in 1966, Bill Russell had succeeded Red Auerbach on the Boston Celtics to become the first Black NBA head coach. In 1974, the Cleveland Indians hired Frank Robinson as baseball’s first Black manager for the following season. Robinson received a congratulatory telegram from President Gerald Ford.

When Shell joined the ranks of Black coaches, sports sociologist Harry Edwards issued what today seems like a prophetic take. “I don’t attach all that much significance to firsts,” he told the Associated Press. “I’m interested in seconds and thirds and fourths and fifths.” He added, “You have to look carefully at what first means in terms of future development because that, in the long run, determines the credibility of the initial move.”

In this Nov. 19, 2006, file photo, Oakland Raiders coach Art Shell works the sidelines during the team’s NFL football game against the Kansas City Chiefs in Kansas City, Mo. Shell was let go by the Raiders following the 1994 season as late owner Al Davis wanted a fresh start for the team for its move back to Oakland. Davis later said he regretted the move and brought Shell back in 2006. Shell had spent his first six years away from the Raiders as an assistant coach but had been out of the profession entirely for five seasons when Davis hired him a second time. AP file photo

Thirty-four years after Shell’s hiring, the NFL — whose players are about 70% Black — continues to lag behind professional basketball and Major League Baseball, which has its own well-documented problems when it comes to hiring Black managers. In the NBA, 14 of 30 teams have Black head coaches, and two of MLB’s 30 teams have Black managers.

Edwards, professor emeritus at the University of California and author of “The Revolt of the Black Athlete,” said in a recent interview that he recognized at the time that Shell’s hiring didn’t represent a league trend.

“This was Mr. Al Davis,” Edwards said, “the same man who had hired the first Latino coach in Tom Flores, who had drafted the first Black quarterback in the first round, and also hired the first woman as a legitimate CEO — Amy Trask. So for him to hire Art Shell was not a surprise to me.”

Shell, who was a star offensive tackle at Maryland State (now the University of Maryland Eastern Shore), went 54-38 in six years in his first stint coaching the Raiders, making the playoffs three times. Like Brian Flores, he was fired after a winning season: His team went 9-7 in 1994, nearly identical to Flores’s 9-8 record last year, before he was dismissed.

“We want to win the Super Bowl,” Davis said at the time. “I felt if we were going to get there, we would have to change the environment.”

There are more recent examples of Black coaches who have been fired after winning seasons. Lovie Smith, who led the Chicago Bears to the Super Bowl in 2007 — where they lost to the Indianapolis Colts, coached by another African American, Tony Dungy — was axed in 2012 after a 10-6 season.

Smith told Washington Post columnist John Feinstein, “Normally you go 10-6, when you meet with your general manager, you think you’re going in to discuss a new contract. It wasn’t quite that way. I got fired.”

The Detroit Lions fired Jim Caldwell after the team finished 9-7 in 2017.

Los Angeles Raiders head coach Art Shell is crowned with a bucket of ice water by Raiders Anthony Smith following the Raiders’ 42-24 win over the Denver Broncos at the Coliseum on Jan 9, 1994, in Los Angeles. AP file photo

Davis later said he regretted firing Shell and brought him back to coach in 2006, raising the number of Black NFL head coaches at the time to seven. But Shell lasted just one season after a 2-14 record. He never coached in the NFL again.

NFL officials have acknowledged the league’s shortcomings. Last month, Troy Vincent, the NFL executive vice president of football operations, told The Post a day after Flores’s dismissal that “there is a double standard” when it comes to retaining and hiring Black coaches in the league. “I don’t think that that is something that we should shy away from,” he said.

In an attempt to get more Black coaches, the NFL in 2003 implemented the Rooney Rule. Named for the late Pittsburgh Steelers owner Dan Rooney, who chaired the league’s diversity committee, it requires teams to interview at least two minority candidates for head coaching openings. It also requires that minorities be considered for front office and coordinator vacancies.

Flores’s suit argues that the rule isn’t working, and there was skepticism about it from the start. In a 2003 Post column, Michael Wilbon wrote that the Rooney Rule “is something that for the most part has been treated as a joke. We expect 18-year-old LeBron James to follow the rules, but grown men who own and run pro football teams get a free pass when they make a mockery of rules?” Referring to a head coach opening on the San Francisco 49ers that went to a White coach, Wilbon questioned whether the team had interviewed two Black candidates merely “as a show” — the same complaint that Flores has leveled at the New York Giants.

Edwards, who works as a consultant for the 49ers and the NFL, said he was never hopeful that the Rooney Rule would have much of an impact. “In some cases, it is indeed the thought that counts, but not in this case.”