ESPN names Cowboys and Giants among five NFL teams most likely to decline

It seems like the Dallas Cowboys and New York Giants are the most popular picks to win the NFC East in 2017. I get it. The Cowboys are coming off a 13-win season while the Giants won 11 games and beat Dallas twice last year.

But just because these teams were good in 2016 doesn’t mean they’re bound to replicate that success this year. In fact, both teams are actually among the NFL teams most likely to decline in 2017. ESPN’s Bill Barnwell recently explained why metrics indicate New York and Dallas are poised to take a step back.

First up, the Giants.

New York’s defense made up for the fact that the offense was trash last year. That defense was much-improved from a unit that was historically awful in 2015. This kind of sudden improvement isn’t always sustainable, as history tells us.

The New York defense improved from 30th to second in both points allowed and DVOA, which is unprecedented in the case of the latter. The previous record was a 27-rank jump, which was pulled off by the 2011 Jaguars. The following year, the Jags fell all the way back to 28th and didn't bound back up toward league average until 2016.

That's an extreme example of what Bill James called the Plexiglass Principle, but teams who suddenly improve like the Giants did often give back some of their gains. Sixteen teams preceding the Giants improved their DVOA rank on defense by 20 spots or more between 1987 and 2015. Those teams declined the next year by an average of just over eight spots in the rankings.

The Giants still have a good deal of defensive talent, so it’s hard to expect them to be suddenly bad. But they could regress a little. Barnwell also points to the Giants’ unusual injury luck last season and the concerns on their offensive line as to why they could win less games in 2017.

The Cowboys’ projected regression is rooted in turnovers.

One of the biggest reasons the Cowboys leaped up the standings in 2016 was their massive improvement in turnover differential. The 2015 Cowboys finished dead last with a turnover margin of minus-22, and we knew this time last year that those teams usually improve significantly the following year. The 2016 Boys were no exception. They improved to a turnover margin of plus-5, a 27-TO swing. Prescott broke Tom Brady's record by starting his career with 176 pass attempts before throwing an interception. An offense with two rookies touching the ball posted the league's fifth-fewest giveaways.

History tells us the sort of leap the Cowboys made almost always gives way to some decline the following season. Teams that improved by 20 or more turnovers in a given season saw their margin decline by more than 11 turnovers the following year. They declined as a group by an average of more than one win. Prescott probably won't post a sub-1 percent interception rate next year. That's reality.

Dallas also has concerns with their defense due to a highly suspect pass rush and question marks in the secondary. The fact that the whole team will likely be suspended or arrested by Week 1 doesn’t help matters.

It’s important to note that ESPN’s projection isn’t saying the Cowboys and Giants will suddenly be bad teams. That’s not what’s going on here. The point is they’re not likely to be as good as they were in 2016.

And it’s that kind of regression to the mean that lines up with a progression to the mean by the Philadelphia Eagles. As BGN’s own James Keane pointed out earlier this year, the Eagles are bound to improve this season. While the Cowboys and Giants benefited from unsustainable factors working in their favor, the Eagles had things working against them.

The result is that the gap has closed. The Eagles were separated from the Giants by four wins last year. They were separated from the Cowboys by six. Their records should be closer this season. The Eagles might even end up being better than both of those teams, or at least one of them.

Philadelphia’s improvement this offseason coinciding with regression from rivals is part of why I feel good about the Eagles’ chances of making the playoffs this year.