The Detroit Lions defense was not good in 2016. In fact, it was arguably the worst defense in the league. They were last in defensive DVOA. They gave up the highest percentage of complete passes in NFL history. They ranked last in passer rating allowed and allowed first downs on the sixth-highest percentage of rushes.

But despite the tower of statistics proving this was a horrible defense, Detroit managed to do something good that they hadn’t done in over 50 years.

#Lions D has held opponents to 20 points or less in 7-straight games in a season for first time since 1961 (Weeks 5-13). pic.twitter.com/xSurF5YWgn — Detroit Lions (@Lions) December 12, 2016

The Lions would actually go on to make it eight straight games the next week, holding the Chicago Bears to just 17 points.

How could a defense this bad go on a streak this impressive? Certainly the opposing offenses had something to do with it, but we’re talking about a streak of 56 years put to bed by the hands of one of the worst defenses in the league. This isn’t just pure coincidence.

So what changed? Many Pride Of Detroiters caught on that while the Lions were holding points to a low total, they were still allowing one of the highest points-per-drive figures in the league. In fact, the Lions still gave up the seventh-most points per drive.

What the Lions had done was simply limit the amount of defensive drives per game. Detroit faced just 155 defensive drives all year, easily the fewest in the league (NFL average was 177). How did the Lions do it? Time of possession on both sides of the ball.

Very interesting: The #Lions had the longest average TOP per drive both on offense (3:10) and defense (3:06). — Pride Of Detroit (@PrideOfDetroit) February 22, 2017

It makes sense that the Lions offense would try to hold onto the ball as long as possible. With such a bad defensive unit, the Lions would obviously prefer to have the offense out there for as long as possible. Keep the bad players off the field.

But is it possible the Lions were intentionally trying to drag out defensive drives, simply to limit the amount of points the opponent could score? And even if that was their strategy, how would the Lions go about trying to do that?

Looking at one important detail of the Lions defense answers both of those questions: snap distribution. Take a look:

Note the drastic change in the use of linebackers starting Week 7 against Washington, not so coincidentally the week the Lions’ streak began. The Lions went from averaging 20.32 percent of defensive snaps claimed by linebackers (or 2.24 linebackers per play) to just 16.79 percent (or just 1.85 linebackers per play).

Just think about that for a second. That’s a huge formation change. The Lions went from averaging two linebackers every play and a third linebacker just about every fourth play, to averaging well under two linebackers per play.

As a result from decreased linebacker play, Detroit utilized their safeties much more, as noted by the highly publicized emergence of Lions safety Miles Killebrew. Detroit went from averaging 2.2 safeties per play to 2.49 safeties per play. In other words, the Lions had a third safety on the field for almost half of their plays after the formation change, as opposed to once every five plays.

That change had drastic effects beyond just limiting the score and lengthening drives; the Lions were also limiting opponents’ efficiency on a per play basis.

Weeks 1-6: 8.24 yards per pass attempt, 4.68 yards per carry , 6.38 yards per play

Weeks 7-15: 6.78 yards per pass attempt, 4.12 yards per carry, 5.32 yards per play

The change in defensive personnel resulted in the Lions allowing a full yard per play less than the linebacker-heavy personnel from the first six games. Detroit improved drastically in the passing game, which is to be expected. When a team relies on big defensive back formations, they are keeping the play in front of them and preventing the long plays.

What is impressive, however, is the huge improvement in the running game. One would think that without heavier players closer to the line of scrimmage, Detroit would have suffered by having an extra man in the secondary. But we, in fact, saw the opposite. With Tavon Wilson, Rafael Bush and Killebrew manning the secondary—all of which have above-average run stopping skills—the Lions actually managed to play better against the run with fewer linebackers on the field.

So what does this mean going forward? Are the Lions going to continue to purposely stretch out games and go safety heavy in 2017?

One clue is how the Lions finished the season. It’s always important to note the personnel a team is dealing with, and much of the reason the Lions likely changed their formation priorities was simply the players at their disposal. Starting with the Washington game, the Lions retired the failed Thurston Armbrister experiment, and by the next week Kyle Van Noy was gone, too. But by the end of the season, the Lions had a relatively healthy Josh Bynes, Tahir Whitehead and DeAndre Levy. As a result, the Lions used linebackers more often toward the end of the season, while safety play decreased*. And with the decreased safety play, the Lions defense collapsed to end the season. Sure, the Lions faced two buzzsaw offenses in the Cowboys and Packers, but their ability to limit big plays evaporated with the drastic change in personnel.

So now the Lions are faced with a dilemma. Should the Lions aim to get better at the linebacker position, or should they simply focus on their more effective safety-heavy formations, where they have budding talent like Tavon Wilson (26) and Miles Killebrew (23)? Obviously, the goal would be to do both, but on a defense with limited talent, the Lions are going to have to make some concessions, and the linebackers may end up suffering because of it.

*Full disclosure: For Week 17, I counted Don Carey’s snaps as a cornerback, since he played the nickel cornerback position for the majority that game.