Romeo Crennel has proven he's one of the NFL's most respected defensive minds.
He's yet to prove he can be a successful head coach.
Doing both of them at the same time? Well, that experiment is off to an embarrassing 0-2 start, leaving just about everyone outside the walls of the Kansas City Chiefs' practice facility to question whether the affable coach is already in over his head.
Asked whether he can successfully handle both jobs, Crennel said, "Yes, I think so," before realizing that perhaps his response didn't sound all that convincing.
"Yes, definitely," he said more steadfastly. "I've done both jobs before. I haven't done both of them at the same time before. I've been a defensive line coach and defensive coordinator before, so I've done dual roles in the past. I kind of understand what it takes."
Being a position coach and coordinator is far different from being a coordinator and head coach, though. The demands aren't nearly as merciless, the scrutiny not nearly as great.
Crennel was Kansas City's defensive coordinator last year, and was promoted to interim coach when Todd Haley was fired. He got the job on a full-time basis, despite going 24-40 in four seasons in Cleveland, but decided to retain his oversight of the defense rather than hire someone else.
So far, the unit that had been one of the NFL's best toward the end of last season has allowed 75 points — tied with Sunday's opponent, New Orleans, for last in the league.
The Chiefs (No. 31 in the AP Pro32) are ranked 17th in pass defense and 26th against the run, a big chunk of that due to C.J. Spiller's virtuoso performance in a 35-17 loss to Buffalo last Sunday.
Veteran linebacker Derrick Johnson doesn't believe anything has changed from last season, and he remains confident that Crennel can continue to juggle two high-profile positions.
"We have a lot of respect for Romeo. He's a guy that's very proven in this league," Johnson said. "I'm a player. I'm a football player. That's a lot of other stuff I don't know nothing about when it comes to coaching. I know when I'm on the field, I have to do X, Y and Z."
There are increasingly few coaches trying to pull double duty in the NFL.
Part of it has to do with the increasingly complex schemes on both sides of the ball. It's no longer enough to run a 3-4 defense against an offense operating out of the I-formation. There are numerous personnel packages and exotic blitzes, and offenses are more dynamic than ever before.
Another difficultly is the stress it places on a coach's time. There are media obligations, events for the public, and in many cases coaches have a big say in personnel decisions, so there is film review and scouting to be done alongside the general manager and front-office staff.
Even within the confines of the practice field, coaches must strike a balance between working with their particular unit and spending time overseeing the team as a whole.
The interim coach of the Saints, Aaron Kromer, is trying to figure out that balance, too.
He continues to serve as offensive line coach while filling as interim head coach during the suspensions of Sean Payton and Joe Vitt for their roles in New Orleans' bounty scandal.
Kromer spends the individual portion of practice working with the offensive line, so there is no head coach roaming around. He takes on a more general oversight role, much like Crennel, during the 11-on-11 portion of practice that is closed to the media.
"Sleeping is optional," Kromer deadpanned.
There are more examples of coaches failing than succeeding when they try to double up.
Raheem Morris was promoted from defensive coordinator to head coach at Tampa Bay in 2009, and then decided to do both jobs when he relieved Jim Bates of coordinator duties in his first season.
Morris went 10-6 in his second season, and for a while appeared to be handling the demands just fine. But the team fell apart last season and Morris was fired in January.
Pat Shurmur also tried to shoulder the responsibility of offensive coordinator in his first season as head coach in Cleveland, but quickly realized how difficult it was to manage both.
The Browns scored just 218 points last season, finished 29th in total yardage and in the lower half of the league in both rushing and passing offense. There often appeared to be communication problems, and Shurmur ultimately decided to hire someone to help with the offense.
He turned the job over to former Vikings head coach Brad Childress.
"There are times when you get in a meeting on the defensive side or offensive side when you could be doing something else at that time, so what happens then is you have both jobs to do," Shurmur said. "You end up staying up a little bit later, you get a lot less sleep, but otherwise I think everybody is capable of doing what they were hired to do."
Crennel said he hasn't considered giving up the coordinator job, even though linebackers coach Gary Gibbs and defensive backs coach Emmitt Thomas have NFL experience in that role.
Crennel simply believes it's a matter of time until the team, and his defense in particular, starts performing up to its level of ability — until guys start doing what he asks of them.
"I think that going forward, we will get better," he said. "If we play the play that we need to play the way we need to play it, then you wouldn't even be asking the question."
AP Sports Writer Tom Withers in Berea, Ohio, contributed to this report.
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