The Detroit Lions' defense is an interesting anomaly.
If you go by total yardage alone, the Lions are a top-15 defense. They're even 12th in passing yards allowed, the area they were most expected to struggle in this year. They're allowing only a 38 percent conversion rate on third downs.
But despite all that, they're giving up the 23rd-most points in the league this year. So, they're somehow both a good defense and a bad defense. What exactly is happening here?
Well, for starters, the Lions appear to have two settings: great defense and no defense. They show signs of both in almost every game they play.
Let's take their most recent performance as an example.
The Houston Texans started 16 drives in their game against the Lions.
Two of those drives were cut off by the ends of the second and fourth quarters. One ended on a missed field goal and one on an interception.
Aside from those four possessions, the Lions forced six three-and-outs, and allowed six scoring drives.
That was the entire defensive performance in a nutshell. If the defense gave up a first down, it either allowed points or time ran out. Nothing in between.
That reflects, fairly accurately, the Lions' biggest strength and weakness on defense. They're a very aggressive, high-risk, high-reward kind of team. That's reflected in its ability to do two things: create negative-yardage plays, or give up big (or especially long intermediate) plays.
In case you were wondering, yes, I am not factoring in Justin Forsett's "81-yard touchdown" run here. There's no point to further discussing how the Lions should stop that than there is in discussing how the Packers should have stopped Golden Tate's game-winning touchdown reception.
In fact, in the Texans game, the Lions maintained discipline in stopping Houston's running attack. Arian Foster earned over 100 yards on the ground, but he didn't reach the mark until halfway through overtime and never recorded more than 15 yards on a single carry.
But the Lions gave up a gain of 20 yards or more on every Texans touchdown drive, and every one of them was a pass to Andre Johnson.
In fact, the first time the Texans earned a first down, in the second quarter, it was on one of those big plays in which they were able to take advantage of the defense's aggressiveness with some misdirection.
Here you can see Matt Schaub running play-action. There are two players in position to make the play here, CB Drayton Florence and DT Sammie Hill.
I've drawn arrows to show you where they're both looking on the play. As a result, here's what that play looks like two seconds later.
Schaub has all day to stand and throw, and more importantly, he has plenty of time to scan the field, and let Andre Johnson get this wide open.
Johnson runs a good route, cutting inside Louis Delmas who has the deep responsibility on him. The result is a 37-yard gain and eventual touchdown.
Beyond that, the Lions appeared to give up a soft spot in the middle of their zone for most of the game.
On the Texans' final drive of regulation, in which they tied the game, they converted two crucial plays that took advantage of the Lions' soft coverage: a 3rd-and-8 from their own 5-yard line, and a 4th-and-7 near midfield. Both were completions to Andre Johnson.
On the first, Johnson sits down in the middle of the field between three defenders, uses his body to shield the safety away from the ball and makes the catch just past the first-down marker.
On the second, Johnson simply makes a quick cut in from the cornerback, again gets inside the safety and again gets enough yardage to keep the drive alive.
Had the Lions stopped either of these plays, it's highly likely the game would have turned out differently for them. Put simply, it's unlikely they would have needed overtime.
Instead, the Lions failed to make the clutch defensive play, the Texans were able to extend their drive on both plays, and the rest is in the record books already.
The Lions have not played well with the lead because of late defensive lapses like this. They lost to the Green Bay Packers despite leading most of the game, and even Jacksonville was able to score a couple times on the Lions prevent defense late in the game.
It seems that the Lions, based on the depth of their safeties, play very aggressively with the front seven but very conservatively with the secondary.
The result is that most short and deep passes are taken away, as is the quarterback's time, but if the quarterback has enough time for a receiver to complete a route, the intermediate area over the middle is available.
That's not a constant, but it is something the Texans feasted on throughout this game. The catch is that it only really works if the pass rush can't get through, and the pass rush for the Lions had been very effective. But in this game, the Texans were able to neutralize the rush often enough to exploit a major vulnerability in the Lions' scheme.
That, or the Lions just had a really hard time matching up with Andre Johnson, in which case they can join the club.