Two-high safety looks took over the 2020 season. Brandon Staley rose from a relative unknown to a star defensive coordinator to head coach thanks, in part, to the structure of his defense. Two-high looks and coverages impacted offenses across the league, including the Kansas City Chiefs and Seattle Seahawks

Under Staley, the Rams had one of the best defenses in the league last season and as is the case with anything that has success in the NFL, the idea is set to spread across the league. Staley’s defense is a variation of Vic Fangio’s, who Staley worked under in Chicago and Denver. Even as offensive coaches across the league have mentioned Fangio’s defenses as among the toughest to play, there had never really been a Fangio coaching tree to spread his concepts across the league.

That tree now has a few branches. With Staley now with the Los Angeles Chargers, he’ll take that defense to another team while the Rams are expected to keep much of that structure in place under new defensive coordinator Raheem Morris. Fangio’s former team, the Bears, promoted Sean Desai to defensive coordinator this offseason. Desai was on staff when Fangio was in Chicago as a quality control coach and he’s expected to keep many of the Fangio principles in his scheme.

While there are going to be more of Fangio’s fingerprints across defenses in 2021, there’s also likely to be some attempts to recreate the scheme without a deeper understanding of what makes it work. When Seattle’s Cover 3 spread across the NFL after the Seahawks had success with the scheme and multiple coaches from that staff moved on to other places, the variants were never as good without the same talent across the defense. Earl Thomas made the single-high coverages work with his sideline-to-sideline range. Richard Sherman was a perfect Cover 3 corner. Bobby Wagner successfully pulled off coverage responsibilities few linebackers in the league could dream of handling. Without pieces like those in place, no team could pull off what Seattle did in that scheme.

The Fangio/Staley system can be slightly more player agnostic (though neither of them lacked talent during the 2020 season) and transferable, but there are so many specifics in play for the defense to work as intended. Tracking the spread of a Fangio scheme will be interesting across the 2021 season because in 2020 it was clear Staley and Fangio were doing something completely different compared to the rest of the league. The below table shows how often a defense lined up in a two-high shell before the snap.

The Rams and Broncos were clearly on their own with a two-high shell on over 75% of defensive snaps, according to Sports Info Solutions (all rates and statistics in this post come from SIS). No other team was over 60% and only three others eclipsed 50%.

But what makes the defense work is not just that the two-high shell turns into Cover 2 or Quarters coverage with two deep safeties playing the pass at a high rate. Both Staley and Fangio use those pre-snap shells to disguise the coverage and still often rotate to a single-high coverage. Below is a chart of how often teams used a pre-snap two-high shell (the same rate as the one above) plotted with how often those teams actually used MOFO (middle of the field open) coverage.

Despite the two-high shell at such a high rate, the Rams ranked just 10th in two-high coverage and the Broncos ranked 14th. Only one team used two-high coverages on at least 50% of their snaps, the Kansas City Chiefs. The Chiefs, though, were only 24th on positive play rate (the percentage of plays that produce positive EPA) when they used two-high coverages.

For the Rams, post-snap rotations worked as they ranked sixth in positive play rate allowed with two-high coverage and third with single-high coverage. The Broncos were eighth in positive play rate allowed middle-of-the-field closed coverage but just 20th in two-high coverages.

The safety rotation worked well in coverage and one of the reasons is how much the structure of the defense works in the run game. The two-high shell presents the opposing offense with a light box, which can make it inviting to run the ball. The secret, of course, is that these defenses have their run fits structured to still be sound and effective against the run while more resources can be used to defend the pass.

In 2020, the Rams showed a light box (six or fewer defenders) on 78% of their defensive snaps, which was the highest rate in the league. With a light box, the Rams had the second-lowest positive play rate allowed and much of that stemmed from how well they played the run. The Rams had a 38% positive play rate allowed on runs plays against a light box. 19 teams had a worse positive play rate allowed on runs against a stacked box (eight or more defenders) in 2020. 

Denver was similar in both metrics. The Broncos showed a light box on 77% of their plays (second-most) and allowed a 38% positive play rate on runs against light boxes.

In this defense, the line plays a gap-and-a-half which still allows linemen to play aggressively but also gives some protection for the second-level defenders who will need to fit the run behind them. Overall, the Rams were second in EPA per attempt allowed against the run in 2020. Denver ranked 21st in EPA per attempt allowed on the ground, but that was due to a few big plays. The Broncos ranked 11th overall in positive play rate allowed against the run.

What gave Staley an advantage there were some of the odd-man fronts he deployed. The Rams’ most used personnel grouping was a 3-3-5 (three linemen, three linebackers, and five defensive backs), though two of those linebackers played on the edge, which produced more of a 5-1 look. Those kinds of fronts were what Fangio used to stop Sean McVay and the Rams during the 2018 season and that idea followed the Rams to the Super Bowl where Bill Belichick and the Patriots adopted the defensive front and Quarters coverage. 

As the wide-zone offense spreads throughout the league under multiple McVay and Kyle Shanahan assistant coaches, having a defense built to have assets to stop the pass and hold up structurally against the run is more than necessary.

That remains the key to this type of structure. This is a defense with run fits built around defending the pass and that gives these pass defenses more leverage to keep the second-level back against intermediate and deep passes. Those are the money areas for offenses and the Rams and Broncos were among the best in limiting effective plays. On pass attempts 11 or more yards past the line of scrimmage, the Rams were first in EPA per play allowed (-0.06, the only team with negative EPA allowed on such throws) and the Broncos ranked sixth.

Each piece of the defense plays a part in why it works so well. Just using a two-high shell isn’t going to cut it. Presenting a light box without the run fits to keep the ground game contained doesn’t make an impact (looking at you, Mike Pettine Packers). We’re going to see more teams try to implement these tactics in an effort to keep up with modern offenses. But how far they dive into the root of what makes the structure work will shape how successful the spread becomes and how big of an impact it could have on offenses throughout the 2021 season.