To borrow Charles Dickens' famous line -- or was it Melania Trump's -- it's the best of times, it's the worst of times for Billy Davis.

The former Eagles defensive coordinator is down in Naples, Fla., living a life of leisure on Jeff Lurie's dime, spending quality time with his wife, Sherry, and their five children, and waking up every morning to a spectacular view of the Gulf of Mexico.

Sounds like the perfect life, and for the better part of the last six months, it was. But Davis is a football coach. And as training camps opened around the NFL last week, Davis couldn't help but wish he was working at one of them.

"It's tough right now," he admitted in a phone interview. "With training camps starting, it's very hard not being a coach and in camp.

"The offseason wasn't hard. The offseason wasn't difficult for me. The time with the family is something coaches never get. My kids are at an age where they want to go play with me every day. I'm coaching them.

"We home-school them a little bit, so I also get to read with them, and do math and things like that. It's been a phenomenal family year. But that was the offseason. These next five months are going to be the hard ones for me. After that, hopefully I'll land somewhere and be back in a coaching chair."

He never saw the punch coming last December. His defense's second-half death spiral was ugly. The Eagles' 7-9 finish was a major disappointment. But never in a million years did he think Lurie would fire Chip Kelly.

"It surprised me," he said. "When your record doesn't meet expectations - which for us last year was the playoffs and beyond -- [getting fired] is always a possibility.

"But I didn't think Chip wouldn't be there anymore, because Jeffrey Lurie has such a long track record of not making those kinds of decisions. He keeps guys for a long time. He likes continuity. I didn't know his feelings [about Kelly] were that strong."

Five coaches from Kelly's staff were retained by Pederson, but Davis wasn't one of them. That hardly was surprising, given his defense's second-half collapse.

In the final eight games, it allowed 33.2 points and 436.5 yards per game. Gave up 23 touchdown passes and 4.89 yards per carry in those last eight games.

"That was one of the biggest mysteries that I was trying to solve," Davis said. "How did we play so good in the first eight [games] and so bad in the last eight? Our confidence was rolling. Other than the Washington game [a 23-20 Week 4 loss] when they had that long [15-play, 90-yard] drive to beat us, we had a pretty solid [first] eight games.

"Then we had some injuries. DeMeco [Ryans]. Nolan Carroll. Jordan [Hicks]. Jordan's injury shouldn't have derailed us as much as it did. But we were really struggling with the linebackers covering the running backs and the tight ends. It poses a lot of problems when you can't get that matchup right."

In the Eagles' first eight games, opposing running backs and tight ends caught 74 passes against the Eagles for just 561 yards and two touchdowns. In the last eight, they had 84 catches for 1,098 yards and 10 touchdowns.

"The pass defense wasn't near where it needed to be," said Davis, whose unit gave up a franchise-record 36 touchdown passes. "But it wasn't all secondary breakdowns. A lot of it was linebackers on running backs, and a couple linebackers on tight ends, that were driving me nuts.

"I thought that was going to be a strength. I thought it was something that wasn't going to be a problem. But Kiko [Alonso] had the knee [injury] and Mychal [Kendricks], sometimes Mychal kind of drifts on you at the wrong time. He makes some great plays, but there are other plays that hurt you."

Kendricks is one of the league's most athletic linebackers. But he plays better when he doesn't have to think a lot. The same with Alonso.

But after Hicks went down with a season-ending pectoral injury against Dallas in Week 10, the Eagles found themselves with a dilemma.

Hicks and Ryans had been the defensive quarterbacks. With Hicks out and Ryans -- slowed by a nagging hamstring injury and at the tail end of his career -- playing limited snaps, Davis found himself having to rely on Kendricks and Alonso to make the defensive calls and make sure everyone was where they were supposed to be.

"One of the things that got us was, one of the inside linebackers needs to be the quarterback," Davis said. "DeMeco was that guy. When he was in there, everybody else just had to worry about [doing] their own job.

"Then DeMeco gets nicked up and goes down and the young kid [Hicks] comes in and does a great job. He was a great quarterback. But then he gets hurt, and now, Mychal or Kiko, one of those two have to be the quarterback. And neither one of them could do that. That's not what they do best.

"When they had to be the quarterback, things changed, and it got a little difficult [for them] to do their own job. You have to line everybody else up and then line yourself up and they couldn't do it.

Alonso was traded to the Dolphins in March along with another major 2015 disappointment, cornerback Byron Maxwell. Kendricks, who signed a four-year, $29 million extension last summer, still is with the Eagles. But Davis thinks he'll play much better for his successor, Jim Schwartz, than he did for him last year.

"I think Mychal will flourish for Jim," he said. "Because he'll be able to just play, like he was able to do for us in 2014. He's highly athletic. He's a great pass rusher. If he can pick up his coverage game, he'll be back to where he was."

Maxwell was another big problem for Davis last year. The Eagles signed him to a six-year, $63 million free-agent deal, hoping he would plug the leak in a secondary that gave up 30 touchdown passes and a league-high 72 pass plays of 20 yards or more the season before.

But Maxwell never was able to deal with the weight and pressure of that big contract. Davis also thinks he had trouble adjusting to Kelly's whole up-tempo approach.

"We needed corners and we felt we had to do it," Davis said of Kelly's decision to give a guy with 17 career starts a $10 million-a-year contract.

"We knew exactly what he was. A long corner. Those long corners don't change directions and move as well [as smaller guys]. But there was so much [good] film on him, [playing] press technique and playing a side and getting a lot of balls thrown his way and being steady and consistent.

"I think a lot of people when you first deal with the no-huddle and how we practice, there's a mental change. I think he struggled with that initially as far as practicing the way we practiced and playing the number of snaps we played. It mentally caught up with him, which was one of the reasons I think it was a hard year for him.

"But there were other parts of it too. It's tough when you go from being a guy in the secondary to being the guy. You put more pressure on yourself. A couple of times, I had to calm him down and tell him to 'stop trying to make the plays to please the city of Philadelphia and make everybody like you. Just play the ball you played in Seattle. Play one down at a time and just do your job and cover your man and it'll all work out.' But I think sometimes he was just trying to do too much. It hurt us."

Thanks to Kelly's up-tempo offense, the Eagles' defense averaged a league-high 71.9 snaps a game last year. Averaged 69.6 in 2014 (second) and also 71.9 in 2013 (first). Davis never used that as an excuse when he was working for Kelly and he's not going to start now.

"We were learning as we went," he said. "I love the no-huddle. It has its challenges. And we were adjusting to those challenges.

"But it's a team game. The offense and their philosophy has to be attached to the defense and its philosophy. We were headed in that direction. We had 10 wins two years in a row. Then we had a little lapse last year and it cost us.

"I would have loved to have had another year to right the wrongs and get it even better. But that didn't happen."