Cowboys can sustain success on D

Back in August, when the available evidence suggested the Dallas Cowboys could be historically bad on defense, I wondered whether the second-string units for teams such as San Francisco might be better. The Cowboys had lost DeMarcus Ware and Sean Lee from a 2013 defense that ranked as one of the league's five worst by just about any valid measure. They had no impact players.

The picture looks quite different now that the Cowboys have a 5-1 record and are coming off a 30-23 road victory over the defending Super Bowl champion Seattle Seahawks. The Cowboys rank near the bottom in defensive categories such as yards per play and sack rate, but they also rank among the top 10 in points allowed, interception rate, first downs per game, passer rating and Total QBR.

This Dallas defense is not terrible. It's been more asset than liability to this point, helping the Cowboys play complementary football while becoming one of the surprise stories in the NFL through Week 6. What's been the key for this Dallas defense and can the Cowboys keep this up? I've collected answers from league insiders, including some whose teams have faced Dallas, and identified a few reasons why it looks like the Cowboys' defense can continue to play well.