Make no mistake, the Kansas City Chiefs defense's performance in the playoffs was a major reason the Chiefs hoisted the Lombardi Trophy last year.
While the Chiefs' offensive comebacks and high-flying theatrics stole the show on the way to KC's first Super Bowl win in 50 years, the defense helped make that outcome even possible.
Due to large special teams gaffes, the Chiefs fell behind 24 points to the Houston Texans in the first half of their divisional round playoff game. The defense gave up only seven points the rest of the game, leading to a comfortable win.
Despite going up against the red-hot Derrick Henry and the Tennessee Titans in the AFC Championship Game, the Chiefs defense made Henry a non-factor and held him to 69 yards rushing.
In the Super Bowl, after a disastrous third and early fourth quarter from the offense, including a late Patrick Mahomes interception, the defense stood their ground and stifled the San Francisco 49ers on four straight drives to seal the Super Bowl victory.
The 2020 Chiefs defense is not playing to that level right now.
The road to the 2019 Chiefs defense performing in the playoffs last year was a bumpy one. The defense was inconsistent and wasn’t finding their footing under new defensive coordinator Steve Spagnuolo.
Using a stat called expected points, the Chiefs defense's progression in 2019 is plainly seen. Expected points (EP) is just the sum of the expected points added (EPA) for every play over the course of the game. Expected points added is based on the down, distance, and outcome of a play. For example, a team is expected to score 2.0 points from 1st and 10 at the 50 yards line. If the team then rushes for 5 yards, leading to 2nd and 5 at the opponent 45, the expected points are now 2.1 points and the play netted +0.1 EPA. A more in-depth dive into EP/EPA is available here and reading about this will start the slow descent down the NFL advanced analytics rabbit hole, so here's the CliffsNotes version: Bigger positive EP is good. Bigger negative EP is bad.
Now, as we emerge from the NFL advanced analytics ether, what does EP tell us about the 2019 Chiefs defense compared to the 2020 Chiefs defense?
The 2019 defense started trending up at this point last year and the 2020 Chiefs defense is doing the opposite.
The 2019 Chiefs defense had up-and-down games, according to EP, in the first part of the year. After a pitiful showing against the Tennessee Titans, however, the Chiefs defense turned a corner and closed the season strong.
Meanwhile, the 2020 Chiefs defense is heading in the wrong direction. After some solid performances at the beginning of the year (minus a major hiccup in the Chiefs' only loss to the Las Vegas Raiders), the Chiefs defense is struggling down the stretch.
One thing to note about the EP stat provided by ProFootballReference; it isn’t opponent-adjusted. While the -6.11 EP looks fine at first glance against the Denver Broncos in Week 13, the Broncos' best offensive EP generated this year was 9.20. The difference of 21.94 EP between the Chiefs' first and second Broncos game is also a chasm.
Now, why has the Chiefs defense fallen off this cliff? There are plenty of possible factors. However, there is one clear area where the Chiefs defense has fallen far behind their performance at this time last year: red-zone defense.
The Chiefs' red-zone defense has been putrid in 2020.
The Chiefs defense is giving up a touchdown in the red zone on 75.8% of trips inside the 20. That mark is good for the worst in the league. The only saving grace for the defense is that they have allowed only 33 trips into the red zone, which is in the top third of the league in that regard.
How did the Chiefs defense fare in 2019 in the red zone? Ninth-best, even though the Chiefs allowed the ninth-most drives into the red zone. Bend but don’t break was how the Chiefs defense operated in 2019. In 2020, the defense has bent less but broken more.
There are also other margins by which the 2020 defense is underperforming compared to the 2019 unit. They allow a score on 2.5% more drives in 2020 and they allow 0.16 more points per drive in 2020 compared to last year.
It’s not all bad news, as the 2020 defense actually forces a turnover on 2% more drives than the 2019 squad. However, the good does not outweigh the bad.
Time is running out for the Chiefs defense to figure out what’s wrong. The turnaround in 2019 happened in Week 11. The Chiefs just finished their Week 13 game. With how crazy this season has been, it’s entirely possible the Chiefs defense and Steve Spagnuolo could make up for lost ground, but these changes have to happen soon.
In the Chiefs' run to the Super Bowl, the defense was clutch when it needed to be. Kansas City didn't bring home the Lombardi on offense alone. So far in 2020, the Chiefs have been carried by a Chiefs offense that is rivaling their production from 2018. Unless Patrick Mahomes and the offense carries the team with an unprecedented playoff run, it’s hard to see the Chiefs running it back with the defense performing how it has in recent weeks. There are still chances for the defense to work out its issues, but it's certainly time for the Chiefs defense to shape up into playoff form.