UNTIL CHIP KELLY holds that long-promised news conference with his entire staff, and presumably fields a few questions, the mystery will linger: Why did it take 3 weeks to hire a defensive coordinator, from a nonplayoff team, who was available even before Kelly was hired?

An NFL source Thursday confirmed the report by Geoff Mosher, of CSNPhilly.com - Bill Davis, the Cleveland Browns' linebackers coach last season, is Kelly's defensive coordinator. Later in the day, the same source confirmed a Footballscoops.com report that Alabama offensive-line coach Jeff Stoutland is coming to the Eagles, so the staff would seem pretty much complete.

The Eagles interviewed Davis, 47, a former defensive coordinator for the 49ers and Cardinals, nearly 2 weeks ago. Why would they take until now to hire him? The most obvious explanation is that they were chasing someone else they couldn't get, for one reason or another.

We know the 49ers denied the Saints permission to talk to secondary coach Ed Donatell for their defensive-coordinator job, a practice not all that uncommon in the NFL. Donatell had been mentioned in Eagles speculation. We know that Georgia defensive coordinator Todd Grantham, also mentioned in connection with the Eagles, decided to make interviewing in New Orleans his priority after apparently refusing NFL interview requests until national signing day passed on Wednesday.

Did the Eagles ask permission to talk to someone from the 49ers or Ravens and not get the OK? Were they interested in Grantham but ultimately decided he wasn't interested enough in them? Was there someone else somewhere we didn't know about, who didn't work out?

We do know that Davis is well-regarded as a linebackers coach - he had D'Qwell Jackson in Cleveland, which didn't hurt - and that he is less well-regarded as a d-coordinator. His San Francisco and Arizona teams finished 32nd, 26th, 20th and 29th in NFL defense. But he was not blessed with great talent in either stop.

Davis has great experience with the 3-4 setup Kelly is thought to prefer. He also has worked with 4-3 schemes, such as the one Cleveland ran last season. Davis described his Arizona defense as a hybrid.

"Everybody puts us in that 3-4 category, but what we are is an 'under' front, a 4-3 'under' defense," Davis said in a 2009 interview. "The 'under' is almost a 3-4." He went on to explain that his front slanted toward the tight end. The gap alignments were slightly different from a 3-4, and one linebacker almost always rushed the passer.

Fans will note that the Eagles now have hired as their offensive and defensive coordinators - unofficially, at least - two guys from the 5-11 Browns, in Pat Shurmur and Davis. Shurmur was the head coach of the Browns, one of four teams actually to lose to the Eagles last season.

But when Kelly was hired, everyone made a big deal of how important it would be for a college coach with no NFL experience to bring in experienced NFL guys as coordinators, and Kelly can't be criticized there - both Shurmur and Davis are longtime NFL coaches who have worked in several league outposts. Both coordinators have Eagles roots, as well. Shurmur was Andy Reid's quarterbacks coach during the Donovan McNabb era. Davis was an Eagles ball boy in the Dick Vermeil years, when he was known as Billy, and his father, Bill Davis, was a Vermeil assistant.

The elder Bill Davis later ran Eagles player personnel for 2 years while Buddy Ryan was the coach; Ryan boasted of being the "real" player personnel chief, and ultimately, of forcing Davis out.

"The situation just hadn't been working out the way either the club anticipated or I anticipated early on," the elder Davis said on the day news of his departure broke, in January 1990. "It was a different kind of situation."

The younger Davis has worked for the Steelers, Panthers, Browns, Packers, Falcons, Giants, 49ers, Cardinals and then the Browns again. Two years ago, when Reid ended up hiring Juan Castillo as his defensive coordinator, Davis was said to have been among the candidates for the job.

Stoutland, meanwhile, might be the biggest staffing coup Kelly has managed. He is a very well-regarded college coach, whose national championship o-line this past season was probably at least as good as what the Eagles fielded most weeks.

Stoutland coached there two seasons, coming from Miami, where he has been among those implicated in the scandal involving booster Nevin Shapiro. A recent Palm Beach Post story said Stoutland is cooperating with NCAA investigators; he was the only Alabama assistant to not get a raise following the 2011 season, in which Stoutland made $395,000.

"I think as a university, we make decisions because we think it's the right thing to do," Alabama coach Nick Saban said in March 2012. "In the future, I think Jeff Stoutland deserves to get a raise based on the merit of the work that he's done here, but I also think it wouldn't be smart on our part to ignore other things that have happened. So, it is what it is."

Stoutland's 2012 Alabama line featured Chance Warmack, a guard who could be among the top half-dozen or so draft prospects; Rimington Trophy winner Barrett Jones as the nation's best center; and tackle D.J. Fluker, who also could be a first-round draft pick this April. The Eagles choose fourth overall, which would be really high to take a guard, even one as highly regarded as Warmack. Also, they have more pressing needs.

"The way Alabama's OL wore down defenses running the ball this past season was something I enjoyed watching," Eagles guard Evan Mathis, a Crimson Tide alum, said Thursday night. "Wouldn't mind Stoutland bringing some of that same mentality to the Eagles."

On Twitter: @LesBowen

Blog: Eagletarian.com