The Denver Broncos lead the NFL in points allowed, yards allowed, defensive sack rate and points scored on defense. More advanced metrics also advocate for Denver possessing the league's best defense through Week 14. The Broncos rank first in expected points added per game, in defensive efficiency per play and in the defensive component of ESPN's Football Power Index, which adjusts for variables such as opponent and venue.
If you're looking for a defense that has been nearly as good as Denver's overall and even better in the past couple of months, the Carolina Panthers could be your choice. The Panthers' defense (which had been covering for the offense before Cam Newton hit his recent MVP stride) ranks first in yards per game, yards per play and defensive EPA per game over the past seven games.
A generation ago, ranking NFL defenses was as simple as flipping through weekly stat packets to see how many yards per game each team allowed. Today, it's as simple as scrolling down to see how I've ranked them heading into the final three weeks of the season. The Broncos get top billing from me, but there is room for debate.
The Broncos' stable of pass-rushers, though diminished by DeMarcus Ware's recent injury troubles, has helped Denver lead the NFL in sack rate, Total QBR allowed and just about every other category.
A dominant defense also explains how the Broncos won their first six games even though Peyton Manning ranked 26th in QBR with a league-high 10 interceptions to that point. Spotty quarterback play caught up to the Broncos when their defense went through a five-game stretch of relatively average play. Dominant performances against San Diego and Oakland during the past two weeks represented a return to form.
Denver's defense is adding 7.7 EPA per game this season, best in the league. That figure ranks seventh out of 320 defenses over the past decade. Carolina is second this season at 6.2 EPA per game, which ranks 16th over the past decade. There's a huge drop to the New York Jets in the third spot at 3.1 EPA per game, making Denver and Carolina clearly the two best defenses this season.
I've become a fan of the EPA metric in recent years for its ability to measure performance in relation to expectation. When a team's offense turns over the ball deep in its own territory, EPA knows the situation carries a high expectation for scoring by the opponent. Allowing points in that situation should not hurt a team's defensive scoring stats as much as allowing a 50-yard touchdown pass would. EPA accounts for this very well.
ESPN's analytics team has more recently developed a "defensive efficiency" metric -- essentially EPA per play with less important plays de-emphasized. Scaling this metric from 0-100 based on a game-level percentile creates a figure representing a team's chances for winning a given game, all else being equal. The Broncos lead the league in defensive efficiency this season at 77.6, just ahead of the Panthers (75.0).
As the ESPN analytics team's recent QBR explainer pointed out, Carolina has allowed only four field goals with no touchdowns on opponents' drives immediately following Newton's 12 turnovers. Newton ranked 27th in QBR and 29th in passer rating through Week 8. Carolina still remained undefeated on the strength of its defense.
Newton has returned the favor recently. He trails only Russell Wilson in QBR since Week 9, having tossed 17 touchdown passes with two interceptions in that span. His improved play bailed out the Panthers' shaky defensive showing against New Orleans in Week 13. (The Saints were responsible for Carolina's two worst defensive EPA performances so far this season.)
The chart below shows Carolina holding a big advantage against the Broncos when both teams' opponents began drives in field goal range, which I defined as the 35-yard line or closer. These are tough situations for defenses, as they often follow swing plays such as turnovers or long returns.
The Broncos allowed five touchdowns and a field goal on the six drives opponents began in this range (I excluded a seventh drive in which Oakland went to kneel-downs to run out the clock). Carolina didn't give up a single touchdown on the eight such drives they faced. But this wasn't quite enough to elevate Carolina into the top spot, as a handful of drives should not override a season's worth of evidence.
The Broncos have allowed 1.26 points per drive overall, compared to 1.35 for the Panthers. And Denver has done it despite facing worse field position on average.
Some of the Chiefs' key defensive players were either at less than full strength or not available at all when the season began, explaining why Kansas City had trouble defensively against Denver, Green Bay and Cincinnati during the first month of the season. The Chiefs lead the league in defensive EPA per game since Week 8. Their average in that span (8.4 EPA per game) exceeds Denver's pace for the full season.
Like the Broncos' defense, the Chiefs' D has fared especially well against the AFC West. Denver is first and Kansas City second in defensive EPA per game against division opponents. For the Chiefs, that includes holding Philip Rivers and San Diego to six total points in two games. Kansas City was fortunate to catch Pittsburgh when Landry Jones was starting for Ben Roethlisberger. Games against Baltimore, Cleveland and Oakland to finish the season provide additional opportunities for the Chiefs to pad their defensive stats.
The Seahawks have faced a higher number of top quarterbacks than the other teams on this list, and they did not fare particularly well against them. Aaron Rodgers (89.2 QBR), Andy Dalton (70.4), Roethlisberger (70.3) and Carson Palmer (68.9) combined to go 3-1 against the Seahawks. Newton (49.5) struggled for much of the Panthers' game at Seattle, but he led a fourth-quarter comeback victory.
Seattle and Carolina are the only teams to lead in the fourth quarters of all 13 games this season. Defensive lapses played a role in the Seahawks losing five of those games, tied with the New York Giants for most games lost after leading in the final quarter. This is still a top-five defense statistically and from a talent standpoint. While Wilson's brilliant play has made headlines recently, note that Seattle's defense has allowed two field goals combined in their past two wins over Minnesota and Baltimore.
The Jets' defense has suffered through only two poor statistical performances this season -- on the road against New England and Oakland in back-to-back weeks. Facing the AFC South and NFC East has certainly helped. Finishing games against New England and Buffalo could prove revealing.