One of the best things about Expected Points Added is that it separates the contributions of offenses, defenses, and special teams. A defense with a very good offense will appear better in terms of other metrics because their opponents would tend to get possession in poor field position. Conversely, a defense sharing a locker room with a below-average offense won't seem as dominant.
Another feature of EPA is that it's measured in net points. It's not just a klugey stat transformed into an analog of net points. It is net point potential. When EPA says a defense is worth 5.0 points per game, that's universally understandable and comparable.
One drawback, at least in its current general implementation, is that EPA doesn't account for the changing nature of the NFL. The league is a moving target, as offenses consistently gain an ever firmer upper hand over defenses. Even over the the last dozen years, offenses have gained several points of advantage. (How do we know exactly how much? EPA, that's how.) So defenses from a decade ago might appear better than today's defenses only because of how the league has evolved.
It's a trivial matter to account for the average EPA by year. That would allow us to compare apples to apples based on the "scoring environment" of the season. I'll do that below and see where SEA '13 fits in. But there's one other notion we should at least consider.
Maybe the change in scoring environment is an outcome rather than a cause. The rules changes have obviously favored offense in several visible ways, and it's hard to argue that's not a factor in the tilt toward offense. However, another contributing factor may be that the better athletes are increasingly being sent to the offensive side of the practice field in high school and college, perhaps to take advantage of the shift in rules and schemes. Young athletes themselves may be choosing offense over defense because of the attention (and money) paid to the skill positions. To whatever degree this is the case, defenses of yesterday may actually be substantially better than the defenses of today. Just a thought.
Back to the Seahawks. Their 2013 defensive EPA, including the entire postseason, was -5.9 points per game. (Negative numbers are good for defenses.) The 2000 Ravens' was -12.9, and the 2002 Bucs' was -10.6, both much better than SEA. But those are the raw EPA numbers, unadjusted for season.
When we adjust for season, things look a lot better for the L.O.B., but not that much. In fact, there are several defenses that come in ahead of Seattle's 2013 squad after adjusting for season. Besides the 2000 BAL squad and the 2002 TB squad, BAL '03, '06, and '08 all finish ahead of SEA. PIT '08 does as well. last year's CHI defense was only a hair behind, and the '09 NYJ defense is right there too. And this year's CIN defense wasn't very far behind SEA. To put things into perspective, the distance between the 2000 BAL defense and the 2013 SEA defense, accounting for era, is about the same as the difference between this year's SEA defense and this year's BUF defense, a very good group but not in the conversation for best ever.
Adjusting for season helps level the playing field, but it's still not completely fair to SEA. [As a Baltimore fan, I wanted to stop right there. But in fairness I had to take the next step.] The Seahawks faced a number of great offenses, including DEN (of course), NO (twice), ATL, IND, SF (3 times) and CAR. Accounting for strength of offensive schedule paints a different picture.
The table below lists the Defensive EPA numbers for the 2000 Ravens, the 2002 Buccaneers, and the 2013 Seahawks. (Reminder: negative is good.) The first column lists the raw unadjusted EPA. The second column adjusts for season, and the third column adjusts for opponent offenses.
Defense EPA (Points per Game)
|Defense||Raw EPA||Season Adjusted||Opponent Adjusted|
The 2000 Ravens are knocked down a peg or two based on an easy regular season lineup of opposing offenses. But they did face a very good DEN offense and an explosive OAK offense in the playoffs, plus a solid NYG offense in the SB. The difference between BAL and TB isn't even as big as 0.1 point per game. That's only due to rounding. It turned out to be -11.69 for BAL and -11.63 for TB. But if you want to split hairs, because they were a wildcard, BAL had 1 more road game than TB (and 2 more than SEA).
I think a lot of fans forget how poor the 2000 BAL offense and (to a lesser degree) the 2002 TB offense were. The 2000 BAL offense went on a streak of 5 consecutive games without a touchdown...and won two of them. Offenses have a lot to do with suppressing opponent scores in several ways, including field position, ball control, turnovers, and forcing opponents to play catch-up. SEA had a solid offense this season, which helped elevate its defense, making them appear a bit more dominant than they were.
A SEA fan would (rightly) point to the fact that his team dominated one of the best offenses in memory on the biggest stage. But BAL and TB did even greater damage, although to lesser opponents. But let's also admit that Manning and his crew had an off night from even before first contact Sunday. For all we know, DEN might have struggled against even an average team.
BAL posted a -30 EPA vs NYG, holding their offense scoreless in the 2000 SB. Think about that for a second. That means the defense alone created 30 points of net score differential. TB posted -25 EPA vs OAK in the 2002 SB, but some of that was 'trash time' stuff. SEA notched just -16 EPA vs DEN, as its offense did the rest. Still, -16 is amazing against an offense that otherwise averaged +15 EPA per game.
It's just too bad we don't have the numbers prior to 1999. I'd love to see how defenses like the '85 Bears would rank, plus the 1914 Pottsville Maroons, and all the other great defenses I'm ignorant of. I'd also love to see how the sport as generally evolved across the decades.
Are the 2013 Seahawks defense the best ever? Of course not. Should they be in the conversation. Definitely not. Unless you're a sports talk radio host, then of course you put them in the conversation! Line 2, you're on the air...