Going into this season, the Kansas City Chiefs’ defense was primarily built on the same players and an influx of rookie talent at cornerback but didn’t see massive schematic change or personnel overhaul. The Chiefs didn’t bring expensive defensive linemen, cornerbacks or linebackers to the team, instead opting for their in-house guys and rookies to fill critical roles.
The only position that underwent an overhaul in free agency was at safety, where the Chiefs opted to let former All-Pro safety Tyrann Mathieu walk, opting to replace him with a younger safety from the Houston Texans Justin Reid. They also drafted safety Bryan Cook in the second round from Cincinnati but didn’t intend on having him take significant snaps in Year 1.
Instead, the Chiefs gave their other starting safety spot to incumbent safety Juan Thornhill. Thornhill was a former 2019 draft pick with flashes of excellent play in his rookie season during the Chiefs' Super Bowl run, but injuries and confidence issues made him more of a rotational player for the Chiefs these last two seasons. Going into this season, Thornhill was the only full-time member of the secondary on that Super Bowl team, so his experience was going to be leaned on.
Neither Reid nor Thornhill played great for extensive portions of the 2022 season. I’ve covered this issue during the season — neither was making plays in the middle of the field nor tackling in space, making them liabilities against the majority of offenses the Chiefs faced. With the way defensive coordinator Steve Spagnuolo calls defense, the Chiefs needed Reid and Thornhill to be able to tackle in space while helping shore up the middle of the field in coverage. Neither was doing it.
Then, a switch flipped in the Week 16 game against the Seattle Seahawks. Suddenly, both Reid and Thornhill were flashing on film consistently. Both started tackling better, getting pressure on blitzes and flying downhill to make plays. Reid and Thornhill were now making plays on the football. They were playing like two veterans in the secondary with elite athleticism, which was something Kansas City missed all season.
So, why the sudden switch in their level of play?
Let’s breakdown the film to try and find out why:
Run defense (from deep and in the box)
The Chiefs play with both of their safeties deep on most of their snaps, making fitting the run difficult. When an offense brings a tight end or fullback into the formation, they can get a numbers advantage against the defense — especially when a quarterback is a threat in the run game.
Defenses have to steal back gaps when they put both their safeties deep. There are many ways of achieving this — going into a Penny front, two-gapping your defensive tackles, or slanting a defensive line — but regardless of what you call, your safeties will have a responsibility in the run fit.
To start the season, the Chiefs struggled to fit the run from two-high because both Reid and Thornhill were late to be force players on the edge and tackle in space. Recently, both have been much better against this.
Reid's run defense has also been good this past month, but his style is a bit different— Nate Christensen (@natech32) January 10, 2023
KC's been rotating safeties in late presnap to fit run or entirely use Reid as box safety, and his tackling and backside chase are good. His tackling has been much more sharp pic.twitter.com/sKivzGhjvl
Reid has recently been a significant positive against the run, whether he’s inserting against the run presnap or postsnap.
The Chiefs have asked him to rotate down into the box against heavier formations and even sometimes insert into the box right before the snap. Recently, he’s done an excellent job getting off blocks and tackling, making him the Chiefs’ best weapon in the box.
Thornhill's also been much better against the run in recent weeks -- whether being a force player from 2H or running the alley in single-high— Nate Christensen (@natech32) January 10, 2023
More willing to drive downhill, tackling significantly improved
Still not elite in run defense by any means but it's still positive pic.twitter.com/7usgoObGxc
Thornhill hasn’t been asked to be in the box much this year, but he still has responsibilities in the run fit. Thornhill is asked to help be a force player off the edge, especially against weak-side runs. When the Chiefs are in a single-high defense, Thornhill has to run the alley and make tackles in space. While he’s never going to be a plus run defender, he’s been much better at tackling and inserting against the run recently, and it helps the Chiefs not leak too many yards against the run.
Thornhill playing from deep
Juan Thornhill's been making more plays in coverage recently, particularly from when the Chiefs are in 2H. He's done a nice job capping vertical routes recently, including two picks capping routes— Nate Christensen (@natech32) January 10, 2023
He's also been driving on crossers against play action, which has been MASSIVE pic.twitter.com/Ehb25lhp1l
Thornhill has had two interceptions in his last three weeks, and while both came off bad throws from quarterbacks, Thornhill has been making more plays in coverage recently.
When he’s been in Cover 2, he’s doing a good job “capping” vertical routes — or staying over the top of them. Thornhill’s range and ball skills stick out there since he can make it all the way to the sideline with his speed.
He’s also been significantly better driving downhill on routes recently, particularly against play-action concepts. When a crossing route emerges, Thornhill flies around to cover it, which has helped the Chiefs against rollouts so much. The Chiefs were just getting picked on with play-action constantly over the majority of the season, but they’ve been much better these past three weeks, and I attribute a lot of that to Thornhill doing such a good job driving on routes.
Reid vs. tight ends in man coverage
In recent weeks, Spags has been much more willing to match Reid up against tight ends in man coverage, whether they're iso'd or as #2 in trips— Nate Christensen (@natech32) January 10, 2023
Reid's got the ideal size to disrupt routes, but also plays ball well
This type of versatility is needed with Sneed/Trent traveling pic.twitter.com/urhQusnRjQ
When the Chiefs decide to play Cover 2 Man as their coverage, they generally ask Reid to cover tight ends in man coverage. They’ll have Reid follow a tight end anywhere, regardless of alignment. Whether a tight end is isolated on the back-side of a formation or the No. 2 receiver in a Trips formation, Reid’s been following the tight end around in passing situations.
The Chiefs have lacked a safety that can man up on a tight end since 2016 Eric Berry — my favorite Chiefs player to watch, ever. Reid has the ideal size to cover tight ends, using his physicality and size to disrupt at the top of routes. He’s also done a better job at the catchpoint, where he’s had multiple pass breakups “working through the hands” when the ball is about to be caught.
This type of versatility allows the Chiefs to have cornerbacks L’Jarius Sneed and Trent McDuffie move around to travel with receivers — something they’ve been doing more recently. If they had a safety that couldn’t cover tight ends individually, they couldn’t do that as well. That level of versatility has helped this defense tremendously.
Reid as a blitzer
One cool 3rd down design: KC showing Cover 3 early, does bail into quarters presnap, I like the simulated pressure design— Nate Christensen (@natech32) December 27, 2022
MIKE mugs A gap and Jones being wide gets a four-man slide, RB responsible for backside S, Reid wins on that rush and Cook's free with protection away pic.twitter.com/eA21kZO2g7
Justin Reid's has been used much more as a blitzer recently, and that makes sense with his size and downhill speed, but he's also been dynamic beating running backs in protection— Nate Christensen (@natech32) January 10, 2023
Good use of swims and chops to get around corner, it's not just running into open space pic.twitter.com/mDfCssvESO
Anyone that’s watched the Chiefs these past few seasons knows how much Spagnuolo loves to blitz his safeties, and Reid’s no stranger to that. He’s been the Chiefs’ main blitzing safety all season and has been pretty good at it. Reid’s speed and explosion downhill are elite, but he’s also capable of beating running backs one-on-one in pass protection.
This ties into his ability to cover tight ends, but since he’s closer to the line of scrimmage on passing downs, that makes it easier to blitz Reid. When they’ve had him blitz, it’s been successful all year, but especially in this recent stretch.
The bottom line
For most of the season, the safety play from the Chiefs wasn’t good enough. That’s a problem, but it also hurt Spagnuolo’s ability to call a defense. He couldn’t trust his safeties to execute anything outside Cover 2, which made the Chiefs' defense predictable. Even in Cover 2, neither safety could insert against the run well, making it hard for the Chiefs to stop the run.
For whatever reason, that all flipped three weeks ago. There’s been way more put on Thornhill and Reid’s plate recently. The number of safety rotations, blitzes and different alignments has increased significantly since the Seahawks game. Not only are they being used in more ways, but they’re also playing much better in every role.
Regardless of what forced that change, the safeties playing better have changed this defense. Spagnuolo can call more plays defensively, which creates more unpredictability. He can afford to have Sneed and McDuffie move around with wide receivers since Reid has been able to play man coverage on tight ends. Reid's ability to blitz is significant because Sneed can no longer be an outside cornerback.
Going into the playoffs, you want to be able to call anything you need to win a game, and with Reid and Thornhill’s better play down the stretch run, the Chiefs' defense has a much better chance at stopping opposing offenses.