Broncos' Defensive Success Unsustainable? Examining the Numbers

The Denver Broncos' defense has been on a roll but is it something fans can count on continuing?

The Denver Broncos' defense has turned things around. After a historically poor start through the first five games of the season, it appeared as if defensive coordinator Vance Joseph was a dead man walking. It also seemed assured the Broncos' defense would sink Sean Payton’s first year as head coach.

Just how bad putrid the Broncos to start the season? Advanced analytics had the Broncos' defense bumbling around with some numbers hardly ever seen in the NFL. 

Through Weeks 1-5, Denver ranked 32nd in EPA/Play at 0.23, 30th in defensive success rate at 48.96%, giving up explosive plays at the highest rate of any team in the league at 14.24% while being equally poor against the pass and run with the 32nd ranked EPA/Pass at 0.33 and the 31st ranked EPA/Rush at 0.10. Anyone with eyes could tell Denver stunk defensively, but the numbers across the board were and still are staggering.

Fortunately, the Broncos' defense turned things around. After a horrible loss 31-21 loss to the New York Jets, where the Broncos gave up 23 points in the second half to what appears to be the singular most incompetent offense in the league, Denver headed on a short week to Kansas City. 

It would have been exceedingly easy to hang their heads and lose that edge needed to compete in the NFL. Instead, the Broncos' defense hung tough against Kansas City and lost 19-8. They say there are no such things as moral victories, but the defense showing up and playing its best game of the season appears to be the catalyst for the defensive turnaround.

That Week 6 loss at Arrowhead was the Broncos' last, as the team has been on an improbable run as of late. Combining the best return game in football, uber ball-control offense, clutch playmaking in the fourth quarter, and what has turned into one of the most opportunistic defenses in football, the Broncos are hot and in the thick of things in the AFC Wildcard hunt.

Since Week 6's loss in Kansas City, the Broncos’ defense sport the 12th-ranked unit in EPA/Play. A massive turnaround from the dead-last unit the team trotted out on the field at the start of this season. What has changed?

Let's examine. 

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The Broncos have gotten healthier on defense with young players emerging and solidifying roles. Losing two of the team's three most consistent back-seven defenders for multiple games early this season led to many assignment errors. 

Without linebacker Josey Jewell and safety Justin Simmons, the Broncos’ run fits and assignments were missed left and right by their replacements as opposing teams exploited the backups. Fortunately, Jewell and Simmons have stayed healthy since returning in Week 6 and have been a stabilizing force for the defense.

Furthermore, the Broncos made some personnel changes that led to much better results on every level of the defense. The return of talented young pass rusher Baron Browning and the exodus of Randy Gregory and Frank Clark have been massive blessings for the Broncos. 

The continued solid play of young rushers Nik Bonitto and Jonathon Cooper has helped Denver’s edge position go from an abject weakness to young and exciting. Hopefully, these young players will continue to grow.

The Broncos' secondary also saw massive turnover. With the outright waiving of early-season starting nickel Essang Bassey and the benching of boundary corner Damarri Mathis, the Broncos switched to blossoming stud Ja’Quan McMillian in the slot and the athletically gifted Fabian Moreau on the boundary. Both have provided a much higher level of play than the missed tackles and blown coverages of their predecessors.

It wasn’t just new players on the field that helped turn around the Broncos' defense. The defense’s biggest acquisition this offseason was defensive lineman Zach Allen, who has also started to play significantly better since the first five games of the season. 

After averaging a Pro Football Focus defensive grade of 61.9 and eight pressures through the first five games, Allen’s average PFF grade is 71.2 with 23 pressures since Week 6. He's playing like a completely different player compared to the first five games of the season.

With how much good the Broncos defense has shown over the last five weeks, some numbers should have Broncos Country nervous about how replicable the defense's performances have been for the unit going forward. Despite having a very solid defense in EPA/Play and points per game since Week 6 this season, the Broncos are still one of the worst defenses in the NFL in Success Rate at 46.89%, ranking 31st.

What is the Success Rate metric? A play is considered successful when it gains 40% of the yards to go on first down, 60% on second down, and 100% on third or fourth down. How could the Broncos’ EPA/Play be so high in comparison to the team’s success rate?

The Broncos may be living on borrowed time in two main categories: takeaway rate and red-zone conversion percentage. Teams are still doing an excellent job moving the ball down the field between 20-yard lines against the Broncos, hence the poor Success Rate, even since the defense started playing at a better clip. The defense’s ability to take the ball away has been incredible, though.

Over the first five weeks of the season, the Broncos took the ball away five times in five games, sporting a turnover differential of -3 over those matchups. Since then, the Broncos have taken the ball away 14 times, including the most in a three-game sample since 1997 (12), and have a turnover differential of +9, meaning they've taken the ball away nine times more than they've given it. 

The Broncos are 5-1 in games this season where they've won the turnover battle and 0-4 in games they have lost it. The rate of turnovers is likely to dwindle, but just winning the turnover battle is key and appears to be a gigantic point of emphasis for Sean Payton and the Broncos on both sides of the ball.

Denver's red-zone defense has also been substantially better in the last five weeks compared to the first five of the season. In Weeks 1-4, the Broncos allowed touchdowns on 13-of-16 red-zone possessions, scoring 81.3 % of the time. 

In Weeks 5-11, Denver has held opponents to touchdowns on 7-of-22 trips inside the red zone, a rate of 31.8%. The Broncos will need to perform better down-to-down in order to combat likely statistical regression in both turnovers and red-zone defense, but the ability to take the ball away and get opponents to stall out when making it inside the 20-yard line is keeping the EPA/Play and Success Rate for the defense far apart.

Bottom Line

The Broncos' defense is certainly playing better football compared to the horrific showing at the start of the season. To the defense’s credit, the team has rallied and started playing a brand of football that can win on Sundays. 

Can the defense play well enough, though, when a team matches Denver in the turnover department and takes advantage of its red-zone opportunities? The discrepancy between the Broncos' defensive EPA/Play to their success rate indicates some level of regression is likely on the horizon for the defense, as the current rate of takeaways is a statistically improbable model for success.

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