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Stats Illustrated: The Stop

Stops are an excellent indicator of a good tackler who excels in making proper reads, and fighting through blocks. This is what a Stop looks like on the field.

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Chicago Bears v Green Bay Packers Photo by Michael Reaves/Getty Images

For most of football history we used pretty terrible stats to rank defensive players. It really came down to tackles and interceptions for a very long time as not even sacks were officially tracked until 1982, and “passes defended” are positively modern. On offense we at least had counting stats like yards and touchdowns (and even passer rating) which, while imperfect, aren’t terrible. On defense, no one really knew anything for like a century.

I’m not sure any set of statistics has come as far in as short of time as those referring to defensive football players. NextGen player tracking data has opened up entirely new avenues to grade defensive backs. The understanding of the importance of pressure has completely changed how we view edge rushers. And thanks to the the concept of the EPA model, we can now quantify how impactful a tackle actually was, which brings us to the “Stop,” which Pro Football Focus describes as:

A stop constitutes a ‘win’ for the defense or conversely a ‘loss’ for the offense. PFF describes a ‘stop’ further as an offensive gain on first down that is kept to less than 40 percent of the line to gain, less than 50 percent of the line to gain on second down and any third- or fourth-down play kept without a first down or touchdown.

Football Outsiders’ uses a similar definition. I have to confess I’m surprised that no site has moved to a model where a stop consists of tackle resulting in a negative EPA play, but, on the other hand, EPA fluctuates greatly based on field position and you may get some wonky results at the extremes. The heuristic used by PFF and FO captures the spirit of the EPA model while treating first downs across the entire field as equal, which does make a fair amount of sense, and is conceptually similar to “success rate.”

As to what constitutes a Stop, in the Packers’ recent game against the Bears there were plenty of examples to choose from, but my favorites were from Rasul Douglas on back to back plays at the start of the second quarter. Douglas is easily the best tackler among the cornerbacks (and at least so far, probably the safeties as well), and on this play on 2nd and 15, he shoots past a would-be blocker to take out Darnell Mooney for a huge 4-yard loss.

Stops aren’t just about sure tackling, they also involve making the correct reads, and correct reactions. It’s worth noting that this play is a bit of a conceptual nightmare from a Bears’ perspective. At the start, Mooney goes in motion and he has everyone’s attention. You can see Douglas staring him down as Savage points behind him.

Savage and Douglas are getting their assignments as pre-motion, Douglas, who is lined up opposite tight end Cole Kmet, had Kmet as his first responsibility. The adjustment allows for Douglas to pass off Kmet and focus on Mooney, which he does.

Motion can be great to get the defense out of sorts, to cause an unanticipated overload to one side, to reveal man v. zone coverage, or to create confusion. This play does none of those things, instead focusing all of the Packers’ attention on the eventual receiver, while motioning poor Mooney into the most heavily defended part of the field. Justin Fields doesn’t help matters with a lackadaisical throw, giving Douglas plenty of time to blow by Kmet and make a sure tackle.

Chicago should burn this play, but someone still needed to clean up the trash, and Douglas did a great job doing so. Rasul Douglas gets the Stop, puts the Bears into a tough 3rd and 19 situation, and costs them almost a full point of EPA. It’s a great job by a great corner.

The next play isn’t as flashy, but Douglas again generates a Stop by working through the Bears blocking and seemingly scaring David Montgomery into a tackle.

This play is a screen pass to the top of the formation, which isn’t the worst idea on 3rd and 19. While a first down is unlikely, perfectly blocked screens are somewhat likely to generate big gains as the secondary is playing back near the sticks, allowing ample room in front of them to theoretically set up blocking, and put the running back into a good position. One missed tackle on a well-executed screen can result in a game-turning conversion, and if nothing else, screens test the discipline of the defense.

Fortunately, it’s still the Bears, and things don’t go well, but they certainly look promising here!

Montgomery has the ball with a full head of steam, plenty of space, and blockers Sam Mustipher (65), Cody Whitehair (67), and Teven Jenkins (76) out ahead of him. He has a solid lead over the chasing Packer defensive linemen. And honestly, if the Bears had better linemen, maybe this play works. Unfortunately for them, they have Bear linemen, and Whitehair and Mustipher are slow getting outside as Darnell Savage, De’Vondre Campbell, and Douglas arrive on the scene. In a perfect world for the Bears, they have 3 blockers taking on three Packers and Montgomery has a clear path to the outside for an impressive first down. Instead, Douglas breaks down in front of Jenkins, who looks completely uninterested in blocking, and instead gives Douglas a playful pat on the back.

Montgomery is either so scared by the now unimpeded Douglas, or so disgusted by the “effort” of his teammate, that he simply goes down in a heap after a modest 7-yard gain. Douglas records another stop, and the Bears are forced to punt.

The current Packer leaders in stops are as follows, per PFF, and while Quay Walker has an impressive number, I do want to use him to point out a problem with Stops, which is that not all Stops are created equal.

While he leads the team with 7, and he has definitely had some important tackles, at least one of those was a tandem tackle where Preston Smith did the real work:

And another was this tackle of Khalil Herbert on the last play of the first half.

It’s a nice read and tackle to be sure, but the play was functionally a kneel down for Chicago. Quay has been good so far, but Stops probably overstates it a bit. Like most stats, it gets better as the sample size grows.

“Stops” isn’t perfect, but it’s a good proxy for identifying sure tacklers who get to their guys, and put them down before they can do any damage. De’Vondre Campbell sitting with only 4, despite playing a position where generating stops is paramount is a good encapsulation of his struggles so far. If you want to know how the defense is doing, and where the weak points may lie, especially upfront, Stops is a good place to start.