The pipeline is all but dry.

Look, as Hue Jackson has, at the numbers. This season, there are only four African-American offensive coordinators and only one, the Tennessee Titans' Terry Robiskie, will call plays. There is only one African-American quarterbacks coach.

After the 2015 season, there were seven head-coaching vacancies. All seven were filled by men who had experience on the offensive side of the ball. Mike Mularkey, Chip Kelly and Jackson had prior head-coaching experience, while Doug Pederson, Ben McAdoo, Adam Gase and Dirk Koetter had been offensive coordinators in 2015.

"My question to you is how on offense is there going to be another potential head-coaching candidate?" Jackson said. "There isn't. So we have to do something to help bridge this gap, and it's incumbent upon us all, because Coach [Marvin] Lewis did it. He put his money where his mouth was with me."

Lewis gave Jackson a shot in 2014, turning over his Cincinnati Bengals offense to Jackson three years after hiring the former Oakland Raiders head coach to be his assistant defensive backs coach.

After the Browns hired Jackson in January to be their eighth head coach since Cleveland returned to the National Football League in 1999, Jackson assembled a coaching staff with minorities in the most important positions. Jackson hired former Indianapolis Colts offensive coordinator Pep Hamilton to be his associate head coach for offense and quarterbacks coach, making Hamilton the only African-American quarterbacks coach in the league this season. Jackson hired former Tennessee defensive coordinator Ray Horton to be his defensive coordinator and former Minnesota Vikings running backs coach Kirby Wilson to be his run-game coordinator and running backs coach.

"It's incumbent upon everybody in the National Football League to reach out and see if there are some men of color who can do the job and give them an opportunity, because I think they are deserving." Hue Jackson, on NFL teams needing to pay attention to all qualified candidates

"There was a time when I was sitting there putting stuff together and going, 'I hope people don't see this the wrong way,'" Jackson said. He knew how it might look, he just didn't care.

"The beautiful part of it is the people within our organization didn't blink," Jackson said. "It was never questioned, 'Hue, you're acquiring too many minorities,' or, 'what are you doing, the people who are in the majority of the lead positions are men of color.'

"I do think it's one of my responsibilities to give back, but as I told many minority coaches, 'I'm going to give back if you're good at what you do. I just can't hand you a job. You have to be one of the best at what you do.' This is the National Football League, and those three guys, to me, are the best at what they do."

But being the best doesn't always matter.

'Good hire for right reasons'

According to research from professors at Georgetown, George Washington, Emory and Iowa State released earlier this year, white position coaches and assistants are more than twice as likely to be promoted to coordinator as their African-American colleagues. Those promotions occur, the researchers found, regardless of the white coaches' performance, experience or coaching background.

That research gave credence to what many minority assistants have felt for years: There's an old boy network in the NFL, where head coaches often hire those whom they know and those with whom they feel comfortable.

With all the progress that has been made since the Rooney Rule was instituted in 2003, mandating that teams must interview one person of color for a head coach or general manager vacancy, there remains work to do. There have been 14 head coaches of color since 2003, and there will be six this season.

While there are nine minority defensive coordinators this season and four minority head coaches with defensive backgrounds, Jackson's point is that there are not enough opportunities for minorities on the offensive side of the ball.

"If you're not coaching the right position in the National Football League, they're not going to find you," Jackson said. "If you don't coach the quarterbacks, if you're not the offensive coordinator, if you're not dealing with calling plays, your chances of ascending the ladder goes way down, and I think everybody knows that. That's a fact."

When John Harbaugh was assembling his first staff in Baltimore in 2008, he reached out to Jackson, who had spent 2007 as Atlanta's offensive coordinator (Jackson didn't call plays there). Harbaugh had heard that Jackson wanted to coach quarterbacks; Jackson had also been Washington's offensive coordinator for one season (also not responsible for calling plays).

Harbaugh didn't really know Jackson, who, as a collegiate quarterback himself, had the reputation of being a straight shooter and a good teacher. As it turned out, the Ravens picked a quarterback -- Joe Flacco -- in the first round of the 2008 draft, and Jackson taught him the fundamentals of playing the position at the highest level.

Pep Hamilton, now the Browns' associate head coach for offense and the quarterbacks coach, has worked with top talents such as Andrew Luck. AP Photo/R Brent Smith

Jackson has said his life changed when Harbaugh allowed him to coach the Ravens quarterbacks.

"I'd met Hue a few times," Harbaugh said. "He was well respected. It's funny because I guess the quarterback coaching thing and the racial part of it, I'm sorry to say I didn't really think about that at the time. It wasn't something that was on my radar that was being a problem or guys weren't doing it. I've seen where he's said that and to get that opportunity he's really appreciative of it, but that wasn't the reason to hire him, I can promise you that. It was because I just thought we had a chance to get one of the best coaches in the National Football League. That's all it was and that's the straightforward truth.

"I guess I'm a little embarrassed I wasn't tuned into it and wasn't thinking about it. On the other side, maybe that's good. But I swear it wasn't like that was part of it. I look back now and it makes me kind of proud, but by the same token, look what he's done. So obviously it was a good hire for the right reasons."

Flacco started all 16 regular-season games and became the first rookie quarterback in NFL history to win two playoff games. Four years later, he won Super Bowl XLVII.

"Hue taught Joe the basics," Harbaugh said. "Here's a quarterback coming out of Delaware, and I don't think he was all that advanced in his football acumen or anything but he was smart, and Hue just built him from the ground up. ... Joe really respected him, and I know he still does."

After two seasons in Baltimore, Jackson became Oakland's offensive coordinator in 2010. He was the Raiders head coach in 2011, the year legendary owner Al Davis died. Oakland started the season 7-4 but lost four of its last five games. After the season, Davis' son Mark hired Reggie McKenzie to be the general manager, and hours into his tenure, McKenzie fired Jackson.

The only job Jackson could get in 2012 was as Cincinnati's defensive backs coach and special-teams assistant. Jackson said he was "disappointed" he had to restart his career on the defensive side of the ball when his area of expertise was offense. It made him doubt the process.

"I did, because I didn't think it would go the way it did," Jackson said. "I don't know how many people, they leave and they have to start totally over. You can't get a job on the side of the ball that you have expertise at. You truly have to start from scratch.

"If it wasn't for Cincinnati, I don't know if I would've had a job. Nobody would talk to me. The only person that would talk to me was Jeff Fisher, but I knew Jeff Fisher was already going to hire Brian Schottenheimer [as offensive coordinator]. It is what it is. But you grow and you get stronger from things, and I wasn't about to give up and say, 'OK, I'm done. Let's go do something else,' because I wanted to prove I could be one of the 32. But you have to work at it."

Said Fisher: "Look at him now."

It's all about opportunities

Jackson made it back, yes, but he had to work his way back to coaching offense in Cincinnati, where he eventually became the offensive coordinator before getting the Cleveland job.

Not everyone, however, ascends. Since there is only one minority who will be coaching quarterbacks this season and likely only one who will be calling plays, Jackson is afraid the pipeline to becoming a head coach from an offensive standpoint is basically dry.

"It's frustrating," said one long-time offensive position coach, who is a minority. "You know there are many [minorities] who want to coach quarterbacks, but because you don't coach that position, you aren't going to get the same opportunities as the guys who do.

"I've heard that about the quarterback thing for the last 10 years. If I had it to do over again, as it relates to me, I would have tried to put myself in the position as a quarterback coach somewhere, because that's the pipeline. There are just more opportunities there."

John Wooten is the chairman of the Fritz Pollard Alliance, a group that works with the NFL as it relates to minority hiring in coaching, scouting and front office positions. Drafted by the Cleveland Browns in 1959, Wooten had a 10-year career and then worked in the front offices of three teams until his retirement in 2002.

Wooten thinks calling plays is "overrated" and points to Harbaugh as an example. Before getting the Baltimore job, Harbaugh was a long-time special-teams coordinator in Philadelphia who spent one season coaching defensive backs.

"I've seen too many successes from being in this league a long time that didn't call plays and yet they go in and do an outstanding job," Wooten said. "If everybody's working together, everybody knows the game plan. If everybody's working together when that draft board is put together, you see how it's done. We know that when you give people an opportunity, it inspires them to work harder, study harder and consequently they end up with a better chance to be successful. That's what breeds success.

"I think the NFL in general now is committed to being a diversified, inclusive league and all that will do is help to make the NFL the greatest sports league in the world, and that's what you really want."

In assembling his coaching staff, Jackson says he targeted the best men, regardless of race, for the job. And that's important, the legendary Jim Brown said.

"I look at it two ways," Brown said. "The first thing is that if the people he hired are qualified and the best people in his mind, I'm for it 100 percent. But if he's hiring them because they're African-American and he wanted to even the playing field, I'm not really for that in that form.

"We're all running to that question of, 'Are we going to make up for the inequities of the past, or are we going to do both?' So as long as we're conscientious about talent and fairness, then I'm for it. I think that unfortunately race is always a factor, and until history shows us or evens the tables, it's going to be a difficult thing to fulfill. So there's no hardcore judgment other than you should hire the best man."

Still, the numbers are what they are. And that's really Jackson's point.

"It's incumbent not just on myself, not Marvin, not Ron Rivera, not Todd Bowles. It's not incumbent upon just us," Jackson said. "It's incumbent upon everybody in the National Football League to reach out and see if there are some men of color who can do the job and give them an opportunity, because I think they are deserving. Some of these guys have been in this league a long time. But if no one's going to talk about it, it's not going to change, and if people aren't willing to talk about it, it's not going to change."

-- NFL Nation reporter Pat McManamon contributed to this story.