Football Outsiders Q&A Part 3: Detroit Lions 2014 defense was a ‘fluke’

In case you missed it, we’re right in the middle of a five part Q&A series with Football Outsider’s Assistant Editor Vincent Verhei. Football Outsiders is an advanced metric site that has detailed analysis on all of the NFL. Every year, the site released their annual almanac, which is chock-full of valuable information. If you’re interested in checking it out, it’s for sale here for $24.95. You can catch parts 1 and 2 or our interview below:

Part 1: Who was responsible for the Detroit Lions’ offensive turnaround in 2015?
Part 2: How much is Theo Riddick worth?

Today, we turn our attention to the defense. The Detroit Lions had one of the best defensive units in 2014, but they took a significant step back last season. So we wanted to know why. Here is Verhei’s answer:

The Lions’ defense dropped from No. 2 in DVOA in 2014 to No. 16 in 2015. What factored into that huge drop? Loss of Ndamukong Suh? DeAndre Levy? Do you see the Lions defense rebounding this year?

The thing is, when you look back at Detroit's recent records, 2015 wasn't the fluke, 2014 was. Going back by season, they were 14th in 2013, 24th in 2012, ninth in 2011, 22nd in 2010, and then the worst defense in football in 2009, 2008, and 2007. So in recent years they have been closer to the middle of the pack than anything else, with the notable exception of 2014.

Looking specifically at the last two years, every indication is that Haloti Ngata was a reasonable fill-in for Suh. The defensive line as a whole was about as good in 2015 as it had been the year before, even better in some areas, but once opposing running backs crossed the line of scrimmage they usually found plenty of running room. We break rush yardage down by several categories, including second level yards per carry, which measures yards gained 5 to 10 yards past the line of scrimmage (so a 5-yard run counts as 1 second level yard, a 6-yard runs counts as 2, on up to 6 second level yards for any gain of 10 yards or more.) The Lions were fifth in the league in second level yards allowed in 2014, but then fell to 28th last year. It would be easy to pin that on the loss of Levy, who is always among the leading linebackers in our individual defense stats, but again when we look back we see 2014 was the fluke year -- the Lions ranked 23rd or worse in this stat every season from 2005 to 2013.

It's harder to pin down the weakness in the pass defense -- aside from sacks, Detroit's numbers were down across the board last season -- but to (finally) answer your question, no, we don't see the Lions' defense rebounding to 2014 levels. We see this as a pretty average defensive side.