In the Rookie Rewind series, we’re taking a look at Kansas City Chiefs players after their first season in the league, focusing specifically their development — and areas that led to improvement or regression in their play. How did they improve from Week 1 — or even college — to the end of their first season? And what does that say about their future?
When the Kansas City Chiefs selected Juan Thornhill with the 63rd pick in the 2019 NFL Draft, lots of hype surrounded him — not just from Chiefs fans, but also from national media voices. He was widely seen as one of the better “value” picks of the draft; plenty of people with league connections spoke about him being a fantastic pick for the Chiefs. As the offseason moved along, it was easy to see why: his football IQ and athleticism really stood out.
By signing free agent safety Tyrann Mathieu — and spending a top 75 pick on Thornhill — the team was attempting to fix one of its weaker position groups. The moves paid big dividends. Mathieu was voted a first-team All Pro defensive back and Thornhill made various All-Rookie team lists.
But in the NFL, playing safety can be a thankless job; hearing your name being called isn’t always a good thing. That’s because a safety’s main job is to keep the offense from getting behind them — in essence, to keep the offense from hitting home-run plays. There isn’t a stat for that. And playing alongside Mathieu — whom the Chiefs often played close to the line of scrimmage — did take away from Thornhill’s ability to stack up other statistics. Just the same, Thornhill ended the year with 57 tackles, five pass breakups and three interceptions — one of which he returned for a touchdown.
Let’s see how Thornhill elevated his game throughout the year, helping the Chiefs finish the regular season strong before his injury in the final week of the season.
From the beginning, Thornhill was a full-time starter, playing 100% of the defensive snaps in the early weeks. Through the games against the Detroit Lions, Indianapolis Colts and Houston Texans, Daniel Sorensen had some snaps — but Thornhill was still the starter and was on the field over 75% of the time; he stepped off the field only situationally or to talk about specific things that had happened.
In the first half of the season, Thornhill’s primary role was as a deep safety; when the Chiefs played a single high coverage shell, he saw the majority of the centerfield reps — both pre-snap and post-snap. When the Chiefs used split-safety looks, he was used almost exclusively as one of the deep-half defenders. While he played well in that role, it was a relatively static deployment — and despite strong play from individuals (including Thornhill), the Chiefs defense wasn’t firing on all cylinders.
After the loss to the Texans in Week 6, the Chiefs began making changes. By the time they came out of the Week 12 bye, they had made the defense much less static; in the next three games, Kendall Fuller returned to action — and we saw more variation in Thornhill’s deployment.
While he remained the predominant deep safety during this stretch, his pre-snap alignment was much more diverse — and based on specific matchups. We also saw changes in his post-snap assignments.
Thornhill rotating to a shaded single high look post-snap. As he's working back to the MoF he I.D.s all three WR's taking an outside release which immediately triggers him towards the SL.— Matt Lane (@ChiefinCarolina) May 28, 2020
Top down angle & early transition allow him to cover both verticals showcasing + range pic.twitter.com/ZjqXmB5bAs
Plays like this show why Thornhill’s IQ and athleticism allows him to excel in deep zone coverage.
Despite the shaded alignment, he’s dropping into single-high coverage — and begins to kick back in that direction. While working for depth, he does a good job keeping his eyes on the trip wide receivers. As soon as all three wideouts are forced into an outside release, Thornhill plants his foot and drives towards the sideline. His angle allows him to help over the top of the seam route — and the fade route along the sideline.
Since he starts out in a shade and the ball is thrown underneath, this play doesn’t look like much — but Thornhill does a great job identifying and reacting to the bunch formation, taking away any chance for a deep throw.
Thornhill working over the top in cone coverage - taking the WR on any in-breaking route or playing deep if the route breaks in/under - does a good job keeping eyes on WR up to the break.— Matt Lane (@ChiefinCarolina) May 28, 2020
Breaks on route then rotates eyes to QB/ball for the INT. pic.twitter.com/WEGT5rgYrn
I charted this play as a “deep half” play — even though it is some kind of cone or box coverage; the man and zone indicators elsewhere on the defense send too many mixed signals for me to say definitively.
The age-old adage is that any safety can play a split-safety defense — but only good ones make plays in them. On this play, this rings true for Thornhill.
If the receiver goes outside or vertical, Thornhill is simply dropping back into a deep-half zone. When the receiver breaks inside, it becomes Thornhill’s job to drive on him or carry him across the field while the cornerback replaces his deep half assignment.
Thornhill’s quick recognition — combined with his athleticism — allow him to beat the wide receiver to the ball, make the pick and return it for points. The coaching staff’s trust in Fuller to play the deep half opposite Thornhill — and in Bashaud Breeland’s ability to replace him as a deep-zone defender — also helped make this play possible.
Mathieu was in man coverage a lot more often than Thornhill who served as the primary deep S but he started rotating down to the LoS later in the year.— Matt Lane (@ChiefinCarolina) May 28, 2020
Flashing the ball skills, speed, and IQ to play in man and zone helped keep the Chiefs' D versatile down the stretch. pic.twitter.com/GzBwVFxvna
As the year went along, Thornhill started getting more reps in man coverage, allowing him to utilize his college cornerback experience. While he wasn’t used much in man, he had just enough snaps that offenses had to account for him dropping into the slot or picking up a receiver behind a blitz. He showed the natural athleticism (and the intelligence) to read a receiver’s leverage and route stems — and make plays on the football.
There are clear man coverage skills - CB experience at Virginia - with his IQ, understanding of leverage, and athleticism to stick on a hip of a receiver.— Matt Lane (@ChiefinCarolina) May 31, 2020
Thornhill could use to be a tick more patient. Working over the stack is hard but wanna try to stay square through the stem. pic.twitter.com/EZ5FFllFLW
It wasn’t always smooth sailing; we sometimes saw the flaws that led to his position change in college. Shiftier players could get him to tilt his hips, taking advantage of the over-aggressive hip opening he would use. As explosive and fast as Thornhill is, his hips aren’t the most fluid; on hard breaks, a lack of patience in staying square to the receiver can hurt him. When needed, he’s still more than capable of playing man coverage — perhaps even more frequently than in 2019 — but it’s not likely he’ll be used like Mathieu has been.
Not a dominant force in the run game - albeit not given a ton of fit responsibilities - Thornhill has shown a knack for making big stops vs the run.— Matt Lane (@ChiefinCarolina) May 31, 2020
Best at running the alley between occupied blockers and utilizing his explosiveness to meet RBs at the LoS with force. pic.twitter.com/P0XlHnDZiR
In 2019, Thornhill’s involvement in the running game was rather limited. Playing as the primary deep safety, he was often left out of the run fit — and when he was involved it was usually as an alley runner where a running back was being funneled to him.
As a rookie, I would say one of his biggest weakness against the run was his tackling technique; he’s a bit of an ankle diver — and while this technique often works in college, it’s much less reliable in the NFL. Still, he did show the ability to be a fine run defender; his athleticism and IQ will always allow him to make some dynamic plays against the run. But we’re not likely to see him characterized as a box safety who specializes in run defense.
Expectations in 2020
If he returns to 100% following his ACL surgery, it’s hard to put a cap on what Juan Thornhill could be. His range and IQ as a single-high safety, ball skills, play-making mentality in the deep half — and his recognition and quick trigger to drive on plays underneath — make him completely scheme-diverse. He can be an impact safety in man coverage, deep zone and underneath zone — all three of the roles in which a safety should proficient — which puts him in rarefied air.
Once Kendall Fuller returned from injury during the latter part of the last season, the Chiefs defense really opened up, exploring Thornhill’s diverse skill set — rather than utilizing him exclusively in his best spot. The plan will almost certainly be to continue the “amoeba secondary” that helped to improve the unit’s performance — but as long as there is a trusted player to take Fuller’s place, expect Thornhill to play an even bigger role.
Having the ability to move Thornhill and Mathieu around — playing all these different techniques — will continue to pressure offenses into making mistakes. And Thornhill has already shown a knack for making big plays.