What matters more: defensive backs or pass-rushers?

After the 2018 season, the Kansas City Chiefs shook up their pass rush and their secondary. How did it pan out, and which unit deserves the focus going forward?

For as long as football has been played, we have seen the power of the trenches. Iconic quarterback-destroyers featured heavily on NFL Films and the TV broadcasts showed what’s going inside their battles with offensive linemen. This gave many the perception that football was won in the trenches. As the data starts to pour in, we are being led to a different conclusion.

The coverage vs. pass rush debate exploded in May 2019 when Pro Football Focus data scientists Eric Eager and George Chahrouri put out their first data study on the topic. Eager followed up with a second edition in August and a third edition in January 2020. These articles took a deep dive into the advanced numbers and showed that, while pass-rushing is more stable and coverage is more volatile, the PFF coverage grades had a clear greater correlation to Expected Points Added (EPA) per pass play and winning percentage than PFF pass-rushing grades.

Despite this study’s findings, many remain unconvinced and may require a specific example to help buy into this idea. Let’s take a look at the Kansas City Chiefs of the Patrick Mahomes era.

In 2018, the Chiefs’ defense was not good. Led by then-defensive coordinator Bob Sutton, the Chiefs’ defense ranked 31st in yards allowed (6,488), 24th in points allowed (421), 31st in passing yards allowed (4,374), 27th in rushing yards allowed (2,114) and 26th in Defense-adjusted Value Over Average (DVOA) (+6.9%). Despite having a terrible defense, the Chiefs actually had the best pass-rush in football. They were first in sacks (57), second in pressures (335), first in PFF Pass Rush grade (90.0) and were the only team to have three or more players reach an 8.5 rating for PFF’s Pass Rushing Productivity (PRP) metric, with Chris Jones at 9.6, Dee Ford at 8.9 and Justin Houston at 8.6.

Following the 2018 season, the Chiefs fired Sutton after six years and brought in Steve Spagnuolo as their new defensive coordinator. They let go of both of their key edge defenders, Dee Ford and Justin Houston, and replaced them with a trio of Frank Clark, Emmanuel Ogbah and Alex Okafor. As a result, the pass-rushing metrics took a massive hit. The Chiefs finished 16th in sacks (45), 13th in pressures (301), 29th in PFF Pass Rush grade (62.9) and had just two players reach a 7.0 PFF PRP rating with Jones at 8.5 and Ogbah at 7.0.

The Chiefs’ shiny new asset coming off the edge, Frank Clark, while playing through a variety of injury issues, did not meet his expectations in the regular season. In 2018, Clark thrived, as he finished tied for 13th in pressures (64), tied for ninth in sacks (13), 33rd in PFF Pass Rush grade (75.2) and tenth in PFF Pass Rushing Productivity (8.7). In 2019, Clark’s production took a nosedive. He finished tied for 49th in pressures (47), tied for 35th in sacks (8), 94th in PFF Pass Rush grade (65.2) and tied for 62nd in PFF Pass Rushing Productivity (6.6). Clark brought it all together in the postseason as his health reached 100%, but the smaller sample size still means that Clark’s 2019 left much to be desired in terms of his own personal production.

One would think this major regression in pass-rushing production would doom the Chiefs defense, but interestingly enough, we saw a different effect. The 2019 Chiefs defense finished the season ranked 17th in yards allowed (5,594), seventh in points allowed (308) and 14th in DVOA (-3.4%), a major improvement from their 2018 stats.

So what could have been the cause of this? Brett Veach put his focus on the secondary. Veach signed do-it-all DB Tyrann Mathieu to a three-year, $42 million deal, drafted Virginia free safety Juan Thornhill with the 63rd pick, and signed cornerback Bashaud Breeland to a one-year, $2 million deal. This immediately turned the safety position, the Chiefs’ most costly weakness from 2018, into a strength on day one of 2019. Mathieu was named a first-team All-Pro by the Associated Press and Thornhill was named to the All-Rookie Team by the Pro Football Writers Association. As a result of their efforts, along with Breeland, Kendall Fuller and Charvarius Ward, the Chiefs finished eighth in passing yards allowed (3,543) and sixth in pass defense DVOA (-9.3%).

In Super Bowl LIV, the Chiefs’ secondary played a major role in the win with two interceptions and just 219 yards passing allowed. On the other hand, the pass-rush left some to be desired, with 13 pressures and one sack. In comparison, the 49ers had 31 pressures and five sacks, but allowed 286 passing yards and two passing touchdowns, both in the late stages of the game in obvious passing situations. In the final 8:33, the Chiefs ran pass plays on 16 of their 19 plays (not including the four kneel-downs to end the game), with two of the run plays coming in that final touchdown drive to give the Chiefs an 11-point lead with 1:12 remaining. On those 16 passing plays, they gained 146 yards. The Chiefs won Super Bowl LIV by effectively passing the ball in crucial situations and effectively stopping the pass in crucial situations.

The 2019 Chiefs, like other recent Super Bowl champions, put many resources towards their secondary and it led to a defense that is more likely to stop a good offense on the big stage. Now that the can of worms has been opened, we can look at these specific examples along with the detailed analytics and come to a smarter conclusion, appreciating the value of a high-quality defensive backfield.

The referenced Pro Football Focus stats are a part of PFF Premium Stats, which comes with a PFF Elite subscription. Go to join.pff.com for more.