Chiefs by the Numbers: Evaluating the Chiefs’ passing defense

In this series, we review the Kansas City Chiefs’ performance primarily using Next Gen Stats (NGS) — along with other advanced metrics that turn up during the season. For any questions on the statistics used in this series, please refer to our Football Analytics Glossary and Metrics page.

The Chiefs’ passing defense

NFL Media’s NFL Pro BETA has a bunch of new stats that will be made available to the public next year. These stats will allow me (and others) to evaluate the league based on the next iteration of Next Gen Stats.

NFL Media

These new metrics reference the commonly used EP and EPA metrics.

Expected Points (EP) is based on the idea that not all yards gained are of equal value. For example: gaining five yards on a third-and-4 — thereby moving the chains — is different than gaining five yards on a second-and-12, which just leads to third down. EP is calculated by comparing the situation — down, distance and field position — at the start of the play to the situation at the end of the play.

Expected Points Added (EPA) is a measure of how well a team performs relative to expectation. For example: a team starts a drive on the opponent’s 40-yard line. Its expected points — the average number of points scored by a team from that spot — would be about 2. If the team then scores a field goal its EPA is found by subtracting its expected points (2) from how the points scored (3). That drive would then have an EPA of 1. But if the team doesn’t score on the drive, it would have an EPA of minus 2.

You’ll notice some new terms in the column headers. Here’s what some of them mean.

• Ball Hawk Percentage (Hawk%) is the defender’s passes defensed and intercepted divided by targets.
• Average Separation (Avg. Sep) is a defender’s average distance from receiver when pass arrives.
• Catch Percentage (Catch%) is the Opponent’s completion percentage when defender is targeted.
• Catch Percentage Over Expected (CROE%) is the Catch Percentage compared to opponent’s completion percentage.
• Coverage Expected Points Added (Cov. EPA) is Expected Points Added when a defender is targeted.
• Tight Window Percentage (TW%) is the percentage of throws attempted into a tight window (defender within half a yard of the receiver) when defender is targeted.

Linebackers

In these metrics, one of the first things that popped out to me is the extremely poor coverage EPA of Kansas City linebacker Nick Bolton at 9.6 (For defensive players, negative numbers are better). That ranks him as the worst regular defender in pass coverage. Bolton is allowing a catch on 84% of the targets thrown his way, with an average separation of 3.9 yards to the player catching the ball. He not creating any tight windows, being within a half yard of his receiver on just 4.7% of his targets.

Bolton’s sidekick Willie Gay Jr. also doesn’t look good in these stats. His coverage EPA of 4.4 isn’t great by league standards, but he’s been better than Bolton. Gay has allowed a catch rate of 90% and an even worse average separation of 4.3 yards. Gay’s tight window percentage of 2.6% is the third-worst among qualified defenders.

The Chiefs need to figure out how to put these two players in a better position to defend passes at the second level. Teams have taken advantage of the Chiefs on short passes to the flat all year — which is made clear by Gay allowing an average of 7.1 yards after the catch on every reception.

Safeties

I have been very critical of the way Kansas City’s safeties have been playing — and according these NGS stats, that criticism is warranted. In coverage EPA, both Juan Thornhill and Justin Reid rank in the bottom third. One of their biggest flaws is an inability to make big plays in the passing game. Reid’s ballhawk percentage is second-worst on the team at 8.3% — which would be fine if he wasn’t giving up big plays. Unfortunately, he has also allowed three touchdowns in coverage. Thornhill has the team’s best ballhawk percentage, but that has still led to only one interception — not enough to counteract the three touchdowns he’s allowed.

Safeties need to be so good in coverage that quarterbacks can’t beat them over the top — and if they aren’t, they should have the ability to bait quarterbacks into throwing interceptions. Kansas City’s safeties aren’t doing either of these things. It’s the defense’s weakest position group.

Cornerbacks

There is some good news. The Chiefs’ cornerbacks are turning in above-average performances — and in the future, could become a very good group.

L’Jarius Sneed is the only Kansas City defender with negative coverage EPA number. Since he is tasked with so many different jobs, his coverage EPA of -3.5 is very good. Working primarily from the slot, Sneed is the defense’s most-targeted player. He allows catches on 70% of his targets and allows an average of five yards after the catch — but he also doesn’t give up many big plays. Given the volume he sees and the role he plays, these are good numbers.

In these metrics, first-round rookie Trent McDuffie is as advertised. He’s allowed catches on just 50% of his targets, has forced a tight window on 32.4% of his targets and has allowed two touchdowns in coverage. Fresh off his worst game as a pro (with a 5.4 in coverage EPA against the Houston Texans last Sunday), McDuffie’s season-long coverage EPA stands at 1.0. If he can find a way to intercept a couple of passes a year, he’d easily be regarded as a top-10 coverage cornerback.

Then there are two other rookie corners — who have probably had much bigger roles than they should have in 2022.

With a coverage EPA of 3.0, seventh-round pick Jaylen Watson has had a very up-and-down season. Watson has given up four touchdowns, but his tight window percentage is 37.7% — the best mark of any defender with more than 300 coverage snaps. While he gets beaten on some plays — and has a lot to learn — Watson has exceeded expectations for a seventh-round selection.

Joshua Williams hasn’t had the same success, but his potential to be a contributor is still there. After allowing five touchdowns, his coverage EPA stands at 7.5. None of his other metrics give a lot of hope for an improvement this season, but Williams wasn’t expected to come out of D-II Fayetteville State and be a contributor on Day 1.

The bottom line

Overall, the Chiefs have some great potential in the defensive secondary — but they are missing a true ballhawk safety who can make the big plays. Coordinator Steve Spagnoulo needs to figure out how to make the linebackers more efficient against the pass — and the team should be using Jaylen Watson more.