In this week's Varsity Numbers, Bill Connelly takes a page out of baseball's playbook and attempts to isolate power from efficiency.
11 Jan 2013
by Danny Tuccitto (SF-GB) and Rivers McCown (ATL-SEA)
Three of DVOA's top five teams square off this weekend for the tickets to the NFC Championship game. Oh, and Atlanta! They're here too.
For those who may be unfamiliar with the Football Outsiders stats, they are explained at the bottom of the page. Scroll down or click this link.
Please remember that all stats represent regular season only, except for weighted DVOA and anything else specifically noted. Any game charting data that appears with a asterisk appears courtesy of the ESPN Stats & Information Group and is complete through the end of the season. Game charting data is still incomplete, but represents roughly 90 percent of the season.
For a scouting perspective, make sure to also check out Andy Benoit's NFC Divisional Round Film Room.
All readers can click here for in-game discussion on our message boards. If you have FO Premium, you can click here to see all the matchup of DVOA splits for this game.
How about the fact that these teams already played in Week 1, but this time it's different? Well, I've heard about this one, but, as we'll learn a little later, the differences likely to matter most aren't among the ones most people are talking about. They involve a of Packers player who hardly played in the first meeting, and a 49ers player who won't play in this game.
Although it's easy to talk about this game as a matchup between the irresistible force of a potent Packers offense versus the immovable object of a formidable 49ers defense, DVOA says both teams rank in the top eight on both offense and defense, and it's basically been that way all season. The ups and downs of individual games produced low DVOA variance rankings, but the larger picture shows two teams playing just as well in recent games as they did early in the season. In other words, this probably won't end up being a redux of last year's 36-32 Divisional Round game between the Saints (great offense) and 49ers (great defense) in Candlestick.
After looking at all of our DVOA splits and charting stats, I've come to firmly believe both offenses have one very clear path to scoring points that trumps all others. Let's start with Green Bay.
As most FO readers are aware, San Francisco is essentially a 12-man unit on defense. If not for Justin Smith's Week 15 injury, they would have had 10 players participating in over 90 percent of their defensive snaps this season. The way it works is that, when the 49ers go to nickel, nose tackle Isaac Sopoaga goes out, cornerback Chris Culliver comes in, and the defense plays in a 2-4-5 alignment. This ironclad tendency holds the key to Green Bay's offensive fortune on Saturday.
Why, you ask? Well, because it implies that San Francisco almost never puts a sixth defensive back on the field, and Green Bay's quartet of Jordy Nelson, James Jones, Randall Cobb, and Greg Jennings makes them one of the few teams that's able (or willing) to field the various four-wide sets (i.e., 01 and 01 personnel groups) requiring dime personnel on defense. So, if the Packers spend as much time as possible in four-wide, it will pit the fourth-best wide receiver corps (17.4% DVOA as a group) against a defense San Francisco rarely practices or plays in games.
Can any non-49ers fans even name San Francisco's dime cornerback? His name is Perrish Cox, and he's participated in only 160 of the 49ers' 1,057 defensive snaps this season (15 percent). Nearly one-third of those (51) came against -- wait for it -- Green Bay in Week 1. Whether because it's his true skill level or he just doesn't get enough playing time is anyone's guess, but Cox is not a good cornerback. In 2010, his success rate in coverage was 49 percent and he allowed 9.1 yards per target. This season, those stats are 25 percent, and 9.8 yards, respectively. It's a much smaller sample size in 2012, but you'd hard pressed to argue he's been significantly better this year. Furthermore, against the Packers in Week 1, he allowed 33 yards and two successful plays on two targets.
Of course, as much as we're able to pin down success/failure in coverage for cornerbacks, defense is still an 11-man dance. As bad as Cox has been individually, San Francisco is much, much better as a unit in nickel than in dime -- yet another fact suggesting Green Bay should go four-wide early and often. This season, the 49ers have faced three-wide sets on 59 percent of plays*, they've responded with nickel personnel on 83 percent of those plays (rest were base), and have given up only 4.9 yards per play (61 percent defensive success rate). In the 14 percent of plays that came against four-wide, however, they were in nickel personnel only 23 percent of the time (rest were dime), and gave up 6.8 yards per play (49 percent defensive success rate).
In Week 1, Green Bay was in a four-wide set on 32 of 61 offensive plays (52 percent). In addition, the three teams besides Green Bay that used four-wide the most against San Francisco are very familiar to them: They all reside in the NFC West (Arizona = 32 percent, Seattle = 12 percent, St. Louis = 9 percent).* Therefore, it's likely all of this isn't just me suggesting a potentially devastating, albeit highly unlikely, strategy. So if they do spend much of the game in four-wide, the question becomes, "Should it be 01 personnel or 10 personnel?" Again, the answer is pretty obvious in light of the stats.
First, there's the one DVOA split in which the Packers have a clear advantage: In red zone passing this season, Green Bay's offense ranked second, while San Francisco's defense ranked 26th. Individually, Jones (70.7% DVOA), Cobb (67.0%), and Jennings (47.1%) in the top six in red zone receiving DVOA among wideouts with eight or more red zone targets, while tight end Jermichael Finley was 18th among tight ends; advantage 10 personnel.
Second, although Green Bay's running game can best be described as "hand waving," they'll be facing a San Francisco run defense that fell off a cliff in the second half of the season. From Week 1 to Week 9, the 49ers run defense DVOA was -29.7%; afterwards, it dropped to -11.3%. By no means have they turned into a below-average unit, but that 18.4% difference was the fifth worst in the league.
The main culprit for this decline seems to be their nickel defense, which -- ironically -- they play so often precisely because the coaching staff believes they can stop the run with only six defenders in the box. According to our charting stats through Week 9, offenses ran on San Francisco's nickel 40 percent of the time, but the 49ers were successful on 69 percent of those plays. From Weeks 10 to 17, however, their success rate dropped to 49 percent while facing an identical run frequency. This was not the case at all for their base 3-4, where their success rate was about 65 percent in both halves of the season. Again, advantage 10 personnel.
Finally, I'd be remiss if I didn't at least mention the Smiths of San Francisco. J.J. Cooper had a nice breakdown in today's Under Pressure and Justin Smith's health has been widely covered this week, so I won't dwell on it. But since we have the game charting available, I'll add this statistical nugget to the conversation: Aldon Smith had a sack, half-sack, or hurry on 9.1 percent of opponent pass plays through 14 games; that dropped to 4.4 percent in the final two.
If it's clear as day that the Packers should spread things out, it's just as clear from our statistics that the 49ers should do the opposite. It's common knowledge by now that San Francisco has the most diverse offense in the NFL from a personnel/formation perspective. For the season, they were in 22 personnel on 24 percent of plays, in 12 personnel on 23 percent, in 11 personnel in 21 percent, and in 21 personnel on -- fittingly -- 21 percent. No other offense uses even three personnel groups with at least 20 percent frequency, let alone four.
In terms of performance, the best of the four is 21 personnel, which has produced 6.4 yards per play and a 54 percent success rate for the offense. It also helps for the purposes of deception that their run-pass frequency in 21 personnel is nearly an even 50-50 split. (For a comparison, they run it 70 percent of the time in 22 personnel, and only 35 percent of the time in 12 personnel.)
Sticking with two-back sets has multiple advantages against Green Bay, not the least of which is how well they worked in Week 1. Similar to the situation with San Francisco's defense, Green Bay plays a ton of nickel; in fact, it's their most frequent personnel group (36 percent). Keeping two backs on the field forces the Packers to play 3-4 base, which the 49ers shredded in the first meeting. In 36 plays with a two-back set against Green Bay's base personnel, San Francisco averaged 6.3 yards per play and was successful 64 percent of the time. Of those plays, their five instances of play-action passing produced 14.8 yards per play and four successes. Contrast this with the 5.4 yards per play and 35 percent success rate on offense when they had one or fewer running backs on the field. For an All-22 breakdown of San Francisco's Week 1 success on "G-Lead" in 21 personnel, see this piece by Matt Bowen of National Football Post.
Of course, you might be screaming at the computer, "but this Green Bay defense is totally different than the one that played in Week 1!" And of course, you'd be right. However, the difference(s) actually work in San Francisco's favor. More so than any of the injuries (Nick Perry and D.J. Smith), the biggest change in Green Bay has been the emergence of Casey Hayward as their slot cornerback in nickel. According to our charting, Hayward had the No. 1 success rate in coverage among cornerbacks this season (72 percent). Pop quiz: For how many of Green Bay's 67 defensive snaps in Week 1 was Hayward on the field? Answer: Five, because he was fourth on the depth chart at the time (behind Jarrett Bush, no less).
So, if the 49ers feature two-back sets, forcing Green Bay to respond with their base 3-4, it keeps the Packers best cornerback off the field. In this light, maybe it's actually a good thing that San Francisco is so woefully thin at wide receiver for the second postseason in a row. With Hayward looking on from the sideline, the 49ers lone threat at wideout, Michael Crabtree, can run routes against Green Bay's worst corner, Tramon Williams, who had a 51 percent success rate in coverage (ranked 58th) and "led" the Packers to a No. 24 ranking against opponents' top wideouts. A word of caution, though: When Green Bay faced a "Calvin Johnson and no one else" Lions pass offense late in the season, Detroit played tight end Tony Scheffler as a slot receiver, which (a) kept Hayward on the field, and (b) rendered Scheffler's presence on it moot. Basically, it would behoove San Francisco to primarily use Vernon Davis as an in-line tight end on Saturday.
If they stick to this game plan of two-back offense, the only real problem for the 49ers is that their running game has taken a nose dive in the second half of the season. Back in Week 6, we were talking about this unit being on pace to produce the best ALY ever. Although they did end up No. 1 this season, their ALY dropped from 5.34 to 4.49 in the final 11 games. In terms of run offense DVOA, San Francisco was 21.7 percentage points worse from Week 10 to Week 17 (2.1%) than they were from Week 1 to Week 9 (23.8%), which was the third largest decline in the league.
What's worse, in four of their past five games, the 49ers have had a run offense DVOA below -20% four times. The origins of that ignominious streak -- indeed what explains the overall decline -- was Kendall Hunter's season-ending injury in Week 12 (i.e., immediately preceding the last five games). Through 11 games, Hunter had the No. 2 DVOA among qualifying running backs (29.5%), which is obviously a huge loss. However, even bigger was the effect his injury had on Frank Gore. Through 11 games, Gore was ranked third with a running back DVOA of 27.9%. (Yes, San Francisco had two of the three most efficient backs in the same backfield.) Over the final five games, Gore ranked 21st with a 2.1% DVOA. Put simply, Brandon Jacobs (since released), Anthony Dixon (better suited for special teams), and even LaMichael James haven't been able to pick up the slack.
With David Akers holding onto his job in San Francisco this week, this game "features" the two worst field goal kickers in the NFL -- the only two with -10 net expected points or worse for the season. If it goes into overtime, this game may never end. Jim Harbaugh has said that Billy Cundiff will likely be inactive, but it wouldn't surprise me if, rather than inactive, Cundiff is used on kickoffs instead of Akers. Last year, Cundiff was the top-ranked kicker in gross kickoff value (+6.4 EPA), second in kickoff distance (69.4 yards), and sixth in touchback percentage (59.5%). Furthermore, before Washington cut Cundiff, the Redskins ranked eighth on kickoffs.
If they chose to go that route, San Francisco would further nullify Cobb's prowess as a returner. Already, Cobb is a better punt returner than kick returner, while the 49ers are better in punt coverage than kick coverage. With Cundiff booting the ball through the end zone -- but of course not through the uprights behind the end zone -- the special teams matchup would be pretty much even stevens. There is one exception, though: Since LaMichael James took over as San Francisco's primary kick returner in Week 14, the unit has improved by 4.0 EPA.
The game plans should be pretty straightforward. For Green Bay, the optimal strategy is to go four-wide given San Francisco's problems in dime and their wide receivers' advantage in the red zone. For a change of pace, they should run it against San Francisco's nickel personnel when possible. In contrast, the 49ers should feature two-back sets with Davis as an in-line tight end, which will keep Hayward off the field and allow Crabtree to match up on Williams. From there, it's run run run, hoping that they've finally figured out how to overcome the loss of Hunter. Finally, special teams shouldn’t play much of a role unless Ted Ginn muffs a punt or one of the two kickers actually finds a way to make a game-winning field goal. As is usually the case (and was the case for San Francisco in last year's playoffs), game plan plus execution equals victory -- unless some special teams randomness dashes all hopes.
All readers can click here for in-game discussion on our message boards. If you have FO Premium, you can click here to see all the matchup of DVOA splits for this game.
Before we begin the analysis of our only bird-on-bird action of the weekend, let's try to get a handle on the Atlanta Falcons. As we've been saying all season, the A-T-L has been dinged in our DVOA ratings because a) they weren't winning many games convincingly and b) they played one of the weakest schedules in the NFL. The -4.3% average DVOA of their opponents was the sixth-easiest slate in the league.
Historically speaking, they are not keeping good company. The 9.1% total DVOA they racked up over the season made them the second-worst 13-win team of the DVOA era, behind only the 1999 Colts. Only the 2009 Chargers and those Colts are even in the same DVOA area code amongst 13-win teams, but for the sake of an arbitrary cutoff, let's double the Falcons' DVOA. Here are how the six other 13-win teams that posted a DVOA under 18.0% fared:
|The Six Worst 13-Win Teams, By DVOA|
|Team||2001 Steelers||2010 Falcons||1999 Titans||2001 Bears||2009 Chargers||2012 Falcons||1999 Colts|
|Playoff Result||Lost to Patriots in AFC Championship Game, 24-17||Lost to Packers in NFC Divisional Round, 48-21||Lost to Rams in Super Bowl, 23-16||Lost to Eagles in NFC Divisional Round, 33-19||Lost to Jets in AFC Divisional Round, 17-14||?||Lost to Titans in AFC Divisional Round, 19-16|
Oh hey, the 2010 Falcons! You guys in Atlanta remember them, right?
Against teams with a better seasonal DVOA than them in their playoff matchups, these teams were a collective 1-5 -- and keep in mind, the 2012 Falcons were worse than most of these teams. The lone win was Tennessee's triumph over Jacksonville in the AFC Championship Game, and those Titans and the 2001 Steelers were the only teams to actually win a game. Seriously, that Titans run to the Super Bowl was graced by luck. People remember the Music City Miracle, but they don't remember that the Bills benched Doug Flutie for Rob Johnson in that game for ... some reason. Then they drew the Colts in the divisional round -- the worst 13-3 team of all-time -- before going to Jacksonville and upsetting them. In 1999, the Rams and Jaguars seemed to be on a collision course to meet in the Super Bowl by DVOA. Jacksonville was more than 10% better by DVOA than the next-best AFC team (Tennessee) that made the playoffs, and the Rams were 7% better than the Jags. The only problem with that was, well, the Titans beat the Jags both times they met in the regular season, handing them their only two losses, then beat them again in the playoffs.
The 2001 Steelers were also the second-best AFC team in the playoffs, but that was a notoriously down year for the AFC. The top-five teams by DVOA were all in the NFC. Pittsburgh didn't play a team they were worse than by DVOA.
So we know what the Falcons are up against historically, but we also know that Seattle is much less impressive on the road, and we know that they'll be playing at 10 a.m. PT, which has been a bit of an issue for all west coast teams over the years. What you might be surprised to know is that Atlanta also had a very sizable home/road split this season. They didn't become a less-effective team, they just became a much different team, and not necessarily in the way you'd imagine:
|Home Cooking on Defense|
|Off DVOA||-8.2% (23)||19.9% (2)|
|Def DVOA||-13.1% (4)||7.3% (23)|
You'd think all those fluid weapons on offense would really spread their wings and fly on offense in the Georgia Dome, but it hasn't played out that way this year. Maybe Atlanta fans are the kind that cheer loudly when their team has the ball -- just kidding, though that does happen in Houston sometimes.
So if you are the type of person to gamble in stations of the world where it is legal, which definitely does not include the city I live in, you might want to consider playing the under in this game.
I think the presumed narrative here, due to the stats presented above, is that Seattle is going to run all over Atlanta's defense. After all, Atlanta finished just 20th in run defense DVOA, and Seattle had the best rushing offense in the league by DVOA. I've already pointed out that Atlanta's defense is completely different at home, but what I didn't point out is that their rush defense also improves significantly at home. Their rush defense DVOA solely in home games is -8.6%, which would put them about 11th on a seasonal level.
However, there are more holes to poke in that "soft run defense" narrative. For one thing, Atlanta's two worst games in rush defense DVOA came in the first three games of the season: Week 1 at Kansas City and Week 3 at San Diego. Additionally, while the game at Washington didn't produce an ugly DVOA rating because the Redskins had the second-best rushing offense by DVOA, it did produce some ugly yardage totals. Well, a major personnel change happened after Atlanta's bye in Week 7, as Ray Edwards ceased to be handed contract-based playing time and was eventually released.
After a few weeks of sorting things out, Atlanta settled on a three-tackle defensive line, moving Jonathan Babineaux outside and letting Corey Peters and Vance Walker handle the inside. This has shored up a majority of their concerns, and they've played much better run defense since the bye:
|Atlanta's Run Defense DVOA|
|Team||Weeks 1-6||Weeks 9-17|
And with even further digging, we find that two of the three worst games in run defense DVOA that Atlanta had post-bye were Week 10 against Dallas and Week 11 at New Orleans. You may remember those games as the ones that star linebacker Sean Weatherspoon missed due to an ankle injury.
This isn't to say that the Seahawks can't run on the Falcons, or that Atlanta won't have trouble slowing down Seattle's zone-read looks -- Carolina and Washington were not easy matchups for this team -- just that the Falcons run defense has been fairly solid since the bye with Weatherspoon in and Edwards gone. I expect Seattle to attempt to run the ball down Atlanta's throat, but I don't necessarily expect a dominant showing from that unit. How effective Seattle's running attack is will go a long way towards deciding this game though, because even though their offense has grown with Russell Wilson, a lot of their passing game is based off play-action.
That's another factor where Atlanta's strengths match up well against Seattle. The Seahawks notched 8.1 yards per pass off non-screen play-action plays this year (7.5 was the average), but a lot of Atlanta's defensive improvement this year came against play-action -- they limited opponents to just 6.6 yards off play-action.* Falcons safeties William Moore and Thomas DeCoud really blossomed under the leadership of new defensive coordinator Mike Nolan. (There is still some question about whether Moore will play in this game though, as he's dealing with a hamstring injury.)
Seattle's biggest weakness this year, as pointed out in last week's preview, was dealing with defensive back blitzes. They picked up just 3.6 yards per play when the defense sent a defensive back at Wilson. Atlanta sent an above-average number of defensive-back blitzes: 12.8 percent versus the league average at 11.4. But they weren't particularly effective when doing so, allowing 6.2 yards per play as compared to the league average of 6.1.*
Don't expect a lot of zone from Atlanta. They are pretty confident in Dunta Robinson and Asante Samuel on the outside. We have them allowing just 15 completions with the "Hole In Zone" marking by our charters. The average is 31. (Samuel tends to play "off-man," which can look like a zone, but it's usually pretty clear he's got the receiver over there.)
The pressing question here is: what does losing Chris Clemons mean for Seattle's pass rush? First-round pick Bruce Irvin seems likely to gain a plurality of the snaps, with rotation linemen like Greg Scruggs stepping in for Red Bryant on passing downs.
While we haven't completed all of this year's charting yet, we have done most of it. Clemons notched 11 sacks to Irvin's eight, but once you factor in some other context, it isn't far-fetched to call Irvin Seattle's best pass-rushing threat. Clemons had 35 of Seattle's 111 charted hurries, or about 31 percent. Irvin had just 18. But Irvin had one less quarterback hit (11) than Clemons did, and, most importantly, Irvin did that in exactly half (434) of the number of snaps (868) Clemons had. (Yes, a lot of those were runs, but that's still quite a few more opportunities for Clemons to rush the passer.) That doesn't mean that losing Clemons won't hurt, but Seattle's pass rush shouldn't be crippled without him.
The real issue with giving more snaps to Irvin is that he came into the league very raw as far as actual defensive-line technique and run defense, and there's nothing in Seattle's usage of him that would suggest he's made major strides with it. Irvin was only in on seven run plays over the course of the entire season, and his average run tackle came 5.3 yards past the line of scrimmage. For reference, the worst any starting Seattle lineman did in that metric was Alan Branch, at 3.8. And Seattle's run defense hasn't exactly been stellar down the stretch with Clemons -- over the first nine weeks of the year, they had a -16.5% rush defense DVOA, and over the last eight, it was 2.7%. The Redskins ran roughshod on Seattle in the first quarter and probably would have continued to do so if not for the fact that their quarterback, through no fault of his own, couldn't hit an open receiver.
Fortunately for Seattle, Atlanta is not the kind of team that can really take advantage of this. Dump truck Michael Turner, Atlanta's "lead back," has been horrendous in advanced metrics this year pretty much any way you slice it. Turner ranked 40th in DYAR and 37th in DVOA out of 43 qualifying backs. Jacquizz Rodgers has actually seen the majority of the snaps in every game since Week 9, but it hasn't made much of a difference. The Falcons had just three weeks with a positive double-digit rush offense by DVOA, and two of those happened in Week 3 and Week 4. Especially galling has been Atlanta's inability to convert in the red zone: the Falcons' -21.2% DVOA on red zone rushes was fifth-worst in the NFL, and 18 of their 37 goal-to-go carries went for no gain or negative yardage.
On this side of the ball, the fireworks will take place in a strength-on-strength matchup between Atlanta's top two wideouts and Seattle's top two corners. While you might think of the Falcons as a team with a lot of pass-catching weapons, they're actually pretty thin at the skill positions once you get past Julio Jones, Roddy White, and Tony Gonzalez. Second tight-end Michael Palmer is almost purely a blocker, adding a fullback has done little for them in the run game this season (3.8 yards per non-scramble attempt out of single-back sets, 3.5 yards per non-scramble attempt with two backs), and third wideout Harry Douglas finished with negative DYAR for the season on the back of a -15.1% DVOA. So despite the fact that Atlanta ran 11-personnel 62 percent of the time,* it was more because Douglas was the best of a bad lot than because he was adding an extra dimension to the offense.
There's not a whole lot of color to add to the White-Jones vs. Brandon Browner and Richard Sherman metagame. All four of them have been phenomenal this season. The Falcons have liked to run screens to Jones to help supplement their run game this season, and he's average 8.8 yards per screen attempt.* But Seattle has allowed just 4.1 yards per attempt on those passes this year -- and just 3.7 yards total on screens once you factor in the ones that go to running backs and tight ends. The Falcons should probably focus more on the receiver that draws Sherman, as he allowed 6.4 yards per attempt as compared to 5.2 for Browner.
Atlanta's special teams were the epitome of mediocre. No unit was worth more than 4.7 points in either direction, and the team as a whole finished with a mighty 0.1% DVOA, good for (you guessed it) 16th in the NFL. The Falcons sorely missed the contributions of former special-teams dynamo Eric Weems, who fled to Chicago last offseason. Jacquizz Rodgers was the primary kick returner, but he had just two returns that went more than 30 yards. Dominique Franks is a very straight-forward punt returner and doesn't dance around much -- only two of his punts returns had negative value. Matt Bryant was actually above-average on pure field-goal value, but once you account for the fact that he played so many games in a dome, he comes out negative in our adjusted metrics.
Seattle, on the other hand, had phenomenal special teams. As Danny pointed out last week, most of the value is concentrated on stopping opposing returns. Time to give Heath Farwell his yearly FO dues for being an awesome special-teams tackler: he tied for fourth in both special-teams tackles and return stops, winding up with an 81 percent Stop Rate. Byron Maxwell and Chris Maragos are also exemplary at ending returns early. Leon Washington has been much better on kick returns than punt returns, and Atlanta has barely been above-average in kickoff coverage, so if a big return is going to change this game, it'll likely come there. It should also be noted that Seattle has lost Steven Hauschka and will use Ryan Longwell on kicks, so that could be a swing in both results and philosophy if Seattle has any fourth-and-short situations in long field-goal range.
Historical numbers will tell you that this is the likeliest "upset" of the weekend. Seattle has been a much better team over the course of the season on a play-by-play basis, certainly. However, digging a little deeper, there are some reasons for Atlanta optimism. As long as Atlanta can prove that they can play the read-option well (something that shouldn't be taken for granted given how successful it was for Washington and Carolina against them this year), their run defense should be better this week than they have been over the course of the season, and that should make this a close game.
Ultimately, the result of this game probably depends on how Atlanta's big receivers play against the best cornerback duo in the NFC. One team decisively winning that matchup will go a long way towards winning the game itself. However, given Atlanta's red-zone problems, it's hard to go against the basic numerical conclusion one would draw from this game: Seattle in a squeaker.
DVOA (Defense-adjusted Value Over Average) breaks down each play of the season and compares it to the NFL average based on situation and opponent. You'll find it explained further here. Since DVOA measures ability to score, a negative DVOA indicates a better defense and worse offense, and a positive DVOA indicates a better offense and worse defense.
SPECIAL TEAMS numbers are different; they represent value in points of extra field position gained compared to NFL average. Field goal rating represents points scored compared to average kicker at same distances. All special teams numbers are adjusted by weather and altitude; the total is then translated into DVOA so it can be compared to offense and defense. Those numbers are explained here.
Each team is listed with DVOA for offense and defense, total along with rush and pass, and rank among the 32 teams in parentheses. (If the DVOA values are difficult to understand, it is easy to just look at the ranks.) We also list red zone DVOA and WEIGHTED DVOA (WEI DVOA), which is based on a formula which drops the value of games early in the season to get a better idea of how teams are playing now (explained here).
Each team also gets a chart showing their performance this year, game-by-game, according to total DVOA. In addition to a line showing each game, another line shows the team's trend for the season, using a rolling average of the last five games. Note that even though the chart appears in the section for when each team has the ball, it represents total performance, not just offense.
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