By Nick Webster
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| T.J. Watt |
Here is a summary of the discussion on defensive statistics in football, crediting Brian Burke for his pioneering work over 15 years ago:
Traditional defensive stats like tackles, sacks, and turnovers forced are limited in scope and typically only measure a single aspect of defensive play. They do not provide a comprehensive view of a player’s defensive contribution. Positive actions (like making a tackle or a sack) can be credited to one player, but missed opportunities or failures by teammates are often not accounted for and defensive plays are frequently team efforts, making it hard to isolate individual performance.
Almost 15 years ago Brian Burke (now of ESPN Stats & Information) in his pioneering Advanced Football Analytics Website suggested using +WPA (Win Probability Added) or +EPA (Expected Points Added, which only considers plays where the defensive player has a positive impact.
The metric essentially captures playmaking ability; however, it does not account for the "hidden" defensive work like coverage that prevents plays from happening or holding blocks.
In his initial work-up, Burke uses the analogy of a corporation +WPA/EPA is like revenue (positive plays), while -WPA/EPA (negative plays) would be expenses, but we can only directly measure the revenue (positive plays) due to data limitations.
Luckily, performance distribution in sports often follows a normal curve where an average defender's performance will be symmetric around their mean, with occasional very good or very bad plays. +WPA/EPA can infer overall performance because good defenders are expected to have more positive plays and fewer negative ones.
Done in 2009 Burke presented a list of top defenders based on +WPA for the 2009 season, showing that players like Jonathan Vilma, Patrick Willis, and Darrelle Revis ranked high, aligning with expert opinions and Pro Bowl selections. Suggesting that +WPA/EPA, despite their limitations, identify key playmakers effectively.
Furthermore, in baseball where it is easier to measure positives and negatives, +WPA correlates strongly with net WPA, suggesting that positive contributions are a good indicator of overall performance. So while +WPA and +EPA do not capture the full spectrum of defensive play, they provide valuable insights into a player's ability to make significant positive contributions and are a useful measure to evaluate defensive performance more objectively overall than traditional stats, as they make it far easier to compare across position groups or even within position groups for players who excel in making different types of impactful plays.
When Burke joined the ESPN Stats & Information Group several years back, he ceased his freelance work and ceased publishing +WPA/EPA for defenders. Luckily, with publicly available data on NFLFastR we can calculate these metrics for more recent seasons. So, what do they tell us about defenders in 2024?
Among interior defenders, the leader in EPA (the defender who made plays that maximally reduced the likelihood of the offense to score) was highly underrated Miami Dolphins Zach Sieler. He’s the portrait of underrated, a 7th-round pick, from a small school (Ferris State) on his second team who has simply improved with every season and now at 29 is among the league's best. I say among as the cluster at the top of interior linemen for EPA is an extraordinarily tight cluster with <5 EPA separating the top four it would be hard to use this information alone to separate among them.
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| Zach Sieler |
Noteworthy, Kobie Turner is on the rise on a young L.A. Rams’ defense that boasts a slew of young talent. Calais Campbell is simply incredible at age 38, he’s now six years older than Aaron Donald was when he hung them up, three years older than Joe Greene and Bob Lilly were, two years older than Merlin Olsen and Alan Page were and of all the Hall of Fame defensive tackles only Ernie Stautner and Leo Nomellini were still in the league at that ripe old age.
Calais should join them in the Hall when he finally decides to hang them up. Also noteworthy is Dexter Lawrence who was robbed of his final 5-games due to injury and likely would have joined the group towards the top of this list.
At the top in WPA were the players making plays that most improved their teams’ chance of winning. Again, imagine a 3rd and 7 sack with the opponent on your own 32, the difference between an almost certain field goal becomes a Punt – if this happens in the fourth quarter in a close game or third quarter in a blowout the EPA is the same, though the former play contributes far more to victory.
The Seahawks’ Leonard Williams leads in this category, and certainly, his 92-yard interception return TD against the Jets was a big contributor. Recall the play happened with the visiting Jets already up 14 points deep in Seahawk territory about to make it a 21-point lead in the middle of the second quarter, in other words, the play turned a would-be blowout into a Seattle one-TD deficit. In fact, when the clock ran down on the game, the Seahawks won 26-21, a five-point victory when Williams had directly scored 6 points!
Not high on either list is Chris Jones, who will garner All-Pro votes and deservingly so as he draws so much attention that allows lesser-known Chiefs to make plays (say thank you George Karlaftis). But with just five sacks, this might be the year we see Cam Heyward and one of the other Interior Linemen sneak through.
Also impactful without making as many plays is the Eagles’ Jalen Carter. He’s a problem for even the best Centers and Guards to deal with and while he may not ultimately make a play that is credited to him, anyone watching the film can see both the talent and the value. The success of the Eagles’ linebacker core is much thanks to Carter.
For years Edge defender, as it's now commonly called, has been one of the most competitive positions with the AP voting three different Edges a DPOY in each of the last three years with Nick Bosa, T.J. Watt then finally Myles Garrett garnering the award. Throw in Maxx Crosby and Micah Parsons nipping at their tails and this has been a group of five fighting for two All-Pro spots for many years. This was a bit of a down year for this group, however, so let’s go to the numbers.
In a relatively down year, it’s clear that despite a late-season swoon following his ankle injury TJ Watt made the most plays costing his opponents points and driving his team closer to victory. Let’s take a moment to deal with who isn’t atop the lists, Myles Garrett had, for him, a somewhat less impactful season – and that could be seen in the overall deterioration in the quality of the Browns’ defense.
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| Myles Garrett |
Injury felled Maxx Crosby and Micah Parsons for meaningful chunks of the season knocking those typical leaders out – and of course, we were robbed of seeing what up-and-comer Aiden Hutchinson could do as he matures to potentially join the topflight. This left TJ at the top, and if you saw him play in the first 14 games, you saw the same on film.
Outside of Watt Greg Rousseau, somewhat similar to Seiler has been consistently improving with every passing year – albeit with the pedigree of a Miami Hurricane picked in the first round. For his length, he plays with great leverage and is excellent at making use of his incredible wingspan. Andrew Van Ginkel and Jonathan Greenard both had outstanding seasons and came in as solid veterans, though one tends to wonder how much of them each breaking out is credit to defensive coordinator Brian Flores whose scheme was the star of the show (until they showed up in Detroit).
Sack leader Trey Hendrickson may appear somewhat lower than many would expect, but he had just 2.5 stuffs (T.J. had 10, Maxx 10.5, Myles 6.5, etc., etc.) and just two FF while Watt led the league in that category with six. He did make many plays, but ultimately the plays Hendrickson made just didn’t impact the game or come at meaningful times, and perhaps that shows in the play of the Bengals Defense overall and the teams’ poor record considering the performance of their QB.
Off-the-ball LB is a very difficult position to judge because it can be played well in so many different ways. Can you tackle, can you cover, can you make plays in the backfield – are your tackles all downfield (somewhere out there a Jesse Tuggle or dare I say it London Fletcher fan is wincing). Where EPA and WPA are nice tools is that not all tackles are created equally. A five-yard tackle on 1st and 10 is a win for the offense, on 3rd and 7 it’s a win for the defense and EPA and WPA would reflect it accordingly – the latter creating value for the defender, the former wouldn’t.
The revelation at LB this season was The Eagles’ Zack Baun – boy those Wisconsin Badgers can grow linebackers. He netted the highest EPA of all defenders in the league and was among the best in contributing to wins. This position group highlights one of the interesting things about EPA vs. WPA. Baun made many plays to stop opponents, but frequently late in the season his team was ahead and protecting leads.
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| Zach Baun |
Meanwhile, Chiefs’ Nick Bolton was good at playmaking by EPA (#10) but as the Chiefs played so many close one-score games his plays were unusually high-leverage. As noted, when discussing interior D-Linemen, both Buan and Bolton probably benefitted from having strong interior linemen who required attention and double teams. Balancing out Baun and Bolton were Zaire Franklin, the Colts’ omnipresent tackling machine and Quincy Williams the Jet who tied a little-known NFL record with five-Stuffs in an otherwise meaningless Week 17 tilt.
Those who watch the game, and know the recent history of the position group won’t be surprised to see Lavonte David (a PFJ favorite and my vote for the most underrated defender of the last 20 years), ageless Bobby Wagner who’s moved up the all-time tackle list (at least since ~1975) to trail only Ray Lewis, London Fletcher and Junior Seau and 49ers superstar Fred Warner on the lists as well.
Warner would certainly have led the list at the quarter pole, and probably even mid-season but played with less abandon as his teams’ hopes faded. David continued to do some of everything, and though he’s a couple steps slower he’s a step more savvy allowing him to still play at a high level. Wagner may be three steps slower and two steps savvier and probably best contributed to turning around the team culture with a Commanders team in need of leaders.
Cornerback is a difficult position group to measure in this manner, typically a corner that does best will have lots of INTs or PDs and sometimes avoiding being targeted yields very little here.
The leader at CB in both EPA and WPA was the outstanding veteran Marlon Humphrey. Patrick Surtain and Derek Stingley were both among league leaders in passer rating allowed and both show up in EPA as does Byron Murphy a credit to his strong tackling and 6 INT’s.
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| Marlon Humphrey |
These metrics love Brian Flores’ Defenses as they're designed to make plays, no ‘bend but don’t break’ in Minnesota these days. Carlton Davis had a very good year in Detroit, by some measures his best, and was the main part in shoring up what was last year a huge liability for the Lions, their pass coverage. Few revelations at the CB position though we should credit Humphrey for his continued playmaking at what’s an advanced age at one of the league’s most physically demanding positions.
At safety Kerby Joseph and Brian Branch (somewhat a slot, really a jack-of-all-trades, DB) both stood out in terms of EPA, they both made plays. Again, these two defenders were frequently making plays with their team ahead and with sizable leads so neither even made the top 10 in WPA. Tre’Von Moehrig and Nick Cross represent solid players who are asked to make a disproportionate number of plays on two quite poor defenses.
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| Kerby Joseph |
C.J. Gardner-Johnson is a difference-maker every time he’s been with the Eagles and made 6 INTs when not frustrating opponents or getting himself ejected. Probably the most interesting case on these lists is Kyle Hamilton, who’s among the most talented safeties in the game but didn’t make a sizable impact in the Ravens’ defense until they shifted to using him deep later in the season.
The Ravens’ defense clearly improved over the course of the season, but it was abundantly clear early that outside of Marlon Humphrey they couldn’t cover any Wideouts, and subsequently they were gashed in the passing game. To Zach Orr’s credit, he adjusted and took his athletic safety who used to play as a 'rover' near the line of scrimmage and played him more in center field using his range to assist an otherwise challenged CB2 and CB3. This worked very effectively and while not a strength the Ravens’ pass defense is no longer the liability it was early in the year, which bodes well heading into the playoffs.
Hopefully, this gave a different view and a different manner of thinking about defenders and the value they produce. It’s simply not always the case that the leading tackler, sacker or interceptor is the best defender in the NFL, they’re asked to do so many different things and the beauty of the EPA/WPA framework is it weights those things based on the relative impact of the play and the context of the play to understand who the best playmakers are and which playmakers most impacted their teams’ drive to victory.
