It's not accurate in every given year, but on the whole, the old adage that defense wins championships holds water. The most recent example, the 2014 Super Bowl champion Seattle Seahawks, led the league in both points allowed and yards allowed in the preceding regular season.

Since the turn of the century, 10 of the 14 Super Bowl champions have finished among the 10 best teams in the league in terms of points allowed, including five teams that ranked atop the list. Nine of the 14 champions have finished the regular season among the 10 best teams in terms of yards allowed.

This year, the Eagles finished far from those lofty heights. Defensive coordinator Bill Davis' unit finished tied for 22nd in terms of points allowed, and 28th in the league in yards allowed.

It was an up-and-down season for the Eagles' defense, but head coach Chip Kelly said he was happy with the way Davis steered the ship during the year.

"I thought Billy did a really good job," Kelly said on Monday morning. "I thought our defense improved in a lot of categories.

"There are still things we need to clean up. We were really good in 2013 in X-plays; we weren't good at all in 2014 in X-plays. I thought our run defense got better. I thought our transition from coming in here and playing a Wide-9, 4-3 defense to a 3-4 defense over last two years ... I think Billy has done a really good job."

Despite registering the team's first shutout in 18 years and finishing the year tied for second in the league in sacks, there are certainly areas in which the unit has to grow, and Davis recognized as much after the team's season finale Sunday.

"We have to get better, and there's no question about that," Davis said bluntly after the Eagles' 34-26 win over the New York Giants. He stood in the visitor's locker room at MetLife Stadium, just a half hour after his defense allowed Giants quarterback Eli Manning to find wide receivers Odell Beckham Jr. and Reuben Randle for a combined 343 yards receiving on 18 catches.

The Eagles' defense surrendered 11 pass plays of 50 yards or more this season, one of which came in the season finale against New York, a 63-yard touchdown pass to Beckham.

While there were improvements in other areas of the defense this season, Davis acknowledged that the secondary's penchant for giving up big plays is one area where the Eagles regressed.

"We've improved in every category except the deep passes," Davis admitted. "And the deep passes are what get the long yards, the touchdowns, the points. So we have to get that fixed, and we will this offseason."

Davis said that there were adjustments he made on Sunday, like having cornerback Cary Williams shadow Beckham, that he could have made earlier in the year.

It's always that way when you finish the season and have a chance to look in the rearview with clear vision, he explained.

"With the benefit of hindsight, looking backwards and knowing the decisions I made didn't work out, you always second guess and say, 'Hey, woulda, coulda, shoulda,' and, 'what if,'" Davis explained. "At the end of the day, I look at it hard, we look at it hard, we study it hard and we make the decision. We've got to make the calls. Sometimes they're right and sometimes they're wrong."

The veteran coordinator isn't pleased with the way things shook out on those X-plays this year, and to make the improvements he said the defense needs, the coaches will be looking at every conceivable part of the defense this offseason.

"We'll look at everything," Davis said. "Every bit of it, from my calls, to the structures, to techniques. There's so many things involved."

And he said he feels good as the team looks to improve going into next year, because of the good things he saw from his team this year, including an excellent year rushing the passer.

Davis also said he thinks he grew as a coach this season, learning from mistakes, and he's confident he and his coaches, along with Kelly, will be able to get their defense working in championship form for next season.

"I think I grew. I really do," Davis said after the game. "I got better. There are games I wish I had back, there are calls I wish I had back.

"I can get better like everybody can get better, and I think I got better this year."