For the second week in a row, the Detroit Lions seemed to play two completely different games: the first half and the second half. The biggest difference between the halves this week was undoubtedly the pass defense. Here's a couple fun little stat lines provided by ESPN's NFL Primetime: 

And then...

Yikes.  So what can we make of this striking difference. Did Romo collapse? Did the Lions make the right defensive adjustments? Did Dallas make the wrong adjustments? Well, the answer is probably somewhere in the middle of all that. I'll look at two similar plays from the first and second halves and show you what happened differently after the jump.

Here's the situation: 

Cowboys' second drive, 3rd and 10 from the Lions' 38 yard line* (no video)

The Lions are playing man-to-man here, with three corners in the game, two linebackers and the safeties in deep zones. The third corner, Brandon McDonald, is the player with running back duty. The play is to Laurent Robinson, who is running the skinny post on the left against Eric Wright. Important to note is the 10-yard cushion that Wright is giving, which seems fine, given that it is third and long. However, Wright literally does not move until Robinson makes his break. By the time he tries to jump the route, it is about half a second too late. This play is well designed, because the route by the tight end gets the linebacker (Stephen Tulloch) out of the area where the ball was going. In fact, Robinson catches the ball almost exactly where Tulloch is standing pre-snap. Delmas tries to get there before Robinson gets to the yellow line but is a second too late, resulting in an easy-looking first down.

Cowboys face 3rd and 2 at Lions' 48 yard line* 

Follow along (at 5:55 mark): 

The Den Lions Vs. Cowboys Slowlights (via Sandman7773)

The formation is nearly the same on both sides of the ball, but flipped. The Lions have the same personnel as the previous play. The biggest difference is that Delmas drops into the box to cover Jason Witten (on the right side of the line) and Tulloch has zone coverage in the middle of the field. Delmas does a good job forcing Witten inside where Tulloch would have likely gotten a hand on a pass to him. However, this play is very well designed from the offensive perspective. Witten's route takes both Delmas and Tulloch out of the way for Robinson's same skinny post route. However, this time Chris Houston is on him and is in his face from the snap, rather than 10 yards back. Obviously, the down and distance has something to do with the tighter coverage, but in general, you saw much tighter coverage in the second half.  

Houston gets his hands on Robinson quickly, disrupting the route. This is key for several reasons. First, by having to adjust his route, Tony Romo cannot be entirely sure where Robinson will be making his cut and it will be much harder for him to guess where the ball should be put. Secondly, Houston has slowed down the play with his physical play, allowing the defensive line more time to get to Romo. When he finally decides to throw the ball, Romo has Cliff Avril (who beat his man to the inside) all up in his grill and Tony is forced to throw off his back foot. Houston, too, beats his man inside and makes a beautiful one-handed interception.

As I said before, the down and distance required a different play call, but regardless, it was nice to see Gunther Cunningham trust his corners, despite the fact that they were getting abused earlier in the game. Increasingly throughout the game, the Lions put more faith in their defenders to go out and make a play rather than waiting for the play to come to them. In the third and fourth quarters, it paid dividends in the form of three turnovers and only three points allowed after the Cowboys' first possession in the second half. 

*Routes by the opposite-side receivers were not displayed because FOX's cameras were too zoomed in to see exactly the routes they were running.