In his previous two stops as an NFL defensive coordinator, Bill Davis was never given a third season. After two years of Davis' middling defense, Chip Kelly brought him back for 2015 despite enough circumstantial evidence that it was time to turn the page.

There was also enough proof to support the notion that he had earned another season, or that the failings of the defense were hardly all his fault. But after 14 games, and woeful outings in three of the last five, it is fair to question whether Davis will be coaching for his job with two games left to play.

"Very confident in Billy Davis," Kelly said Monday, a day after the Eagles' 40-17 loss to the Cardinals.

Kelly staunchly backed Davis after the Buccaneers and Lions posted 45 points apiece on the Eagles in November. The defense, in turn, rebounded against the Patriots and the Bills. So his support should come as no surprise. And it's not as if the defense has been solely responsible for a 6-8 record. Kelly's offense has been inconsistent all season.

But the marginal improvement that Davis' unit has made in pass defense has been offset by a steep decline against the run. And all things being equal, the numbers this season compared with his first two seasons have been worse in many key categories - red zone, third down, and most important, points. Tackling also has gotten progressively worse.

Saturday's win-or-don't-make-the-playoffs showdown with the Redskins could be a referendum on Davis, his scheme and his play calling. A year ago, the Eagles faced a similar scenario, and his penchant for leaving his outside cornerbacks in man-to-man situations with only a single-high safety over top burned the team.

DeSean Jackson caught four passes for 126 yards and twice smoked Bradley Fletcher. The Packers and second Cowboys games also hammered down the point that the Eagles needed to upgrade the secondary.

So Kelly signed Byron Maxwell to a $10 million-a-year contract. He rolled the dice on Walter Thurmond and converted him to safety. And he drafted Eric Rowe in the second round. The Eagles also hired Cory Undlin to be their new defensive backs coach.

The changes paid off, but not significantly. The Eagles have allowed 6.67 yards per pass attempt vs. 7.17 yards last season and 6.92 yards in 2013. They rank 13th in the league in that category after finishing 22d and 20th in the two previous years, respectively.

Limiting the X-play (passes longer than 20 yards) has been one of the defensive success stories this season. The Eagles have permitted only 3.4 X-plays compared with a last-in-the-NFL 4.5 last season. But they also have already matched last year's total of 30 touchdowns surrendered through the air.

Adding injury to insult, the Eagles could be without both Maxwell (shoulder) and Rowe (concussion) on Saturday. E.J. Biggers and Jaylen Watkins filled in for both against the Cardinals, and while they acquitted themselves fairly well in coverage, they both missed several open field tackles.

Davis was intent on preventing Carson Palmer from beating the Eagles deep. And he mostly succeeded. The Cardinals quarterback completed only 1 of 9 passes that traveled more than 20 yards. But that was about all the defense did right.

Arizona's success on the ground was most disconcerting. Rookie David Johnson rushed for 187 yards and three touchdowns on 29 carries. The Eagles allowed 230 rushing yards overall. While the run defense has been worse since rookie linebacker Jordan Hicks tore his pectoral muscle - 4.1 yards per rush before and 5.0 yards after - it has been a season-long issue.

The two previous seasons combined, the Eagles allowed only 3.7 yards per carry on the ground. This year, they've allowed 4.5 yards per rush. They went from second in the league through six games to 27th.

The defensive front hasn't been as dominant at the point of attack as it was earlier in the season. Bennie Logan hasn't been the same since suffering a knee injury. But Fletcher Cox has made up for some of the deficiencies.

The bigger problem has been at the second level with the inside linebackers. DeMeco Ryans, at 31 years old, has lost much of his burst. Mychal Kendricks, who signed a four-year contract extension in August, has been undisciplined.

And Kiko Alonso, acquired in the trade for LeSean McCoy, has been a virtual nonfactor since returning from arthroscopic knee surgery.

"I know he can do it, he knows he can do it," Kelly said. "We just need to do it on a more consistent basis."

It's hard to look at the inside linebacker group, though, and blame Davis. He isn't the general manager. And he can't go out there and tackle. The Eagles missed 15 would-be tackles against the Cardinals, according to Pro Football Focus.

Tackling has been sound for most of the season, but there also were poor showings against the Bucs and Lions. Kelly agreed with a questioner that some players are trying to go for the strip rather than properly wrapping up.

"We are not doing a good enough job coaching that," Kelly said.

That falls partially on Davis' shoulders. But what he is most responsible for is putting his players in the right positions, and there have been enough examples of when he has failed to do so.

On Johnson's first 1-yard touchdown run, Davis sent his nickel package in right before the snap. He was matching the Cardinals, who had three receivers on the field. But to do so in a goal-line situation on second down may have been overthinking personnel.

Thurmond was pitted against 6-foot-7, 281-pound tight end Darren Fells, and Johnson ran right behind him untouched into the end zone. Whether there was an on-field miscommunication or not, Davis gambled and lost.

The numbers aren't in his favor.