Beware the Use of Sack Statistics

| August 2, 2009

The phrase “a little knowledge is a dangerous thing” rings true in many facets of life but when I hear it I always think of the statistic sacks. In the history of the NFL, I’m not sure there’s been as misunderstood or abused a number.

In itself it’s fine: “the number of times a quarterback, in the act of passing, is tackled for a loss.” However, because of lack of other data, people have used it for a myriad of things on which it has little, if any bearing:

1. The pass-protection capability of an offense
2. The ability of an offensive lineman
3. The skill of a pass rusher

The point is that sacks are only a minor subset of pressure. Last season, across the league, they accounted for only 16 percent of all pressure when hits and pressure on the QB are included. A hit is when a QB is knocked down but not sacked and a pressure is when a QB is forced to move in the pocket in some other way than simply stepping up into it to throw.

So what does pressure do to a QB? Well, when pressured or hit, a player’s QB rating is reduced by an average of 37 points. That’s the equivalent of turning Peyton Manning into Brad Johnson on every single play involving pressure. Interestingly, while it’s great for the team, sacking a QB doesn’t alter the opposing quarterback’s rating.

So if pressure, not sacks, is the key stat how does this affect our view of the NFL and where have we been misled?

A. The pass protection capability of an offense

Unfortunately, when the media refer to the protection capability of an offense, it’s almost always based on sacks allowed. You’ll see nearly every commentator or pundit quote it in reference to how good an offensive line is playing. This in itself neglects the role played by tight ends, running backs and, most importantly, quarterbacks. More on that later. The bottom line in protection is reduction of pressure, so for this we need the total number of times pressured (sacks, hits and pressures combined) and the total number of times a QB dropped back to pass. Below is the percentage of times teams gave up pressure on a passing play during 2008:

Team — Pressure/Passing Play
1. Tennessee — 26.02 percent
2. New York Jets — 27.59 percent
3. Carolina — 29.35 percent
4. New York Giants — 31.43 percent
5. St. Louis — 31.55 percent
6. Denver — 32.80 percent
7. Tampa Bay — 33.12 percent
8. Atlanta — 33.33 percent
9. Miami — 33.45 percent
10. New Orleans — 33.97 percent
11. Kansas City — 34.13 percent
12. Philadelphia — 34.83 percent
13. Chicago — 35.85 percent
14. Cleveland — 36.07 percent
15. Indianapolis — 37.05 percent
16. Green Bay — 37.09 percent
17. Cincinnati — 37.24 percent
18. New England — 37.66 percent
19. San Diego — 38.00 percent
20. Houston — 38.13 percent
21. Baltimore — 38.18 percent
22. Oakland — 40.77 percent
23. Buffalo — 41.11 percent
24. Arizona — 41.80 percent
25. Washington — 41.90 percent
26. Minnesota — 43.01 percent
27. San Francisco — 44.69 percent
28. Jacksonville — 45.77 percent
29. Detroit — 46.45 percent
30 Pittsburgh — 47.71 percent
31. Dallas — 48.64 percent
32. Seattle — 50.18 percent

The key message here is that teams like New Orleans, Indianapolis and Denver (which people perceive as having excellent pass protection because they give up a remarkably low number of sacks) aren’t at the top of the list any more, and the Colts are mid-table. So what’s the difference? We believe it’s the QB, although not — as many may think — based on scrambling ability. It’s much more to do with understanding the defense, pocket presence and quick release. You only need to watch a handful of games to see Manning, Drew Brees or Jay Cutler reading the situation and delivering the ball in such a way as to avoid the sack. In the 1980s Dan Marino took very few sacks despite pressure because of the player he was. I sometimes wonder just what Peyton could do if he had his brother’s line in front of him; I’m not sure another team would get close.

By contrast to the first list, here’s the best to worst from last year in terms of allowing pressure to be turned into sacks:

Team — Sacks/Total Pressure
1. Indianapolis — 6.02 percent
2. New Orleans — 6.06 percent
3. Denver — 6.61 percent
4. Tennessee — 8.57 percent
5. Arizona — 10.03 percent
6. Philadelphia — 11.11 percent
7. Atlanta — 12.29 percent
8. Dallas — 12.94 percent
9. Seattle — 13.55 percent
10. Cleveland — 13.64 percent
11. Houston — 14.41 percent
12. San Diego — 14.83 percent
13. Green Bay — 14.98 percent
14. Jacksonville — 15.41 percent
15. Miami — 15.54 percent
16. Chicago — 15.79 percent
17. Kansas City — 15.81 percent
18. Tampa Bay — 16.11 percent
19. Carolina — 16.55 percent
20. Baltimore — 16.81 percent
21. New York Giants — 17.58 percent
22. Buffalo — 18.34 percent
23. Washington — 18.73 percent
24. San Francisco — 19.78 percent
25. Pittsburgh — 19.82 percent
26. Oakland — 19.90 percent
27. Detroit — 20.28 percent
28. New York Jets — 20.61 percent
29. Minnesota — 21.14 percent
30. New England — 22.55 percent
31. Cincinnati — 24.02 percent
32. St. Louis — 25.40 percent

Of the first five teams on that list, only Cutler could be termed a mobile QB. But that isn’t to say it makes no difference. I’m sure Jacksonville and Seattle would have more sacks with their porous lines if it wasn’t for the mobility of David Garrard and Seneca Wallace, respectively.

B. The ability of an offensive lineman

I was watching the usually excellent Cris Collinsworth lamenting in the Week 15 Saints at Bears game that the pressure on Brees was far worse because Jammal Brown wasn’t in at LT. Zach Strief was starting because Brown was injured. During the season, Brown gave up pressure on 8 percent of all passing plays and Strief 5 percent, but in that game 7 percent. What Collinsworth could have said was the pressure on Brees was worse because the usually excellent Jahri Evans had a poor game, but that’s not so obvious. Far easier to go with the old standby that the backup isn’t up to the standard of the Pro Bowl player whose reputation hasn’t diminished despite being awful for the last two seasons. Why? Because Brees doesn’t give up sacks even though he’s under pressure from both edges. Last year Brown gave up only 3 sacks but also 15 hits and 28 pressures. Jon Stinchcomb gave up only 1 sack but allowed 10 hits and a whopping 37 pressures.

Other players who fall into this category are the hugely overrated Tony Ugoh (whose run blocking deteriorated as well last year) with 3 sacks but 11 hits and 29 pressures. Both of Denver’s new tackles picked up rave reviews for their pass blocking based on giving up 0.5 of a sack and 2.5 sacks. The idea of how you give up half a sack aside, what this misses is accompanying hits and pressures. Only one tackle gave up more than Ryan Harris’ 38 pressures in 2008. You guessed it: Ryan Clady, with 39.

The best pass-protecting tackle last year? The unheralded David Stewart who gave up 3 sacks but pressure on only 2.97 percent of passes. The worst? The 49ers RT, Adam Snyder, who gave up 8 sacks but pressure on 11.6 percent of plays despite spending much of his time at guard.

C. The skill of a pass rusher

Taking things from a different perspective, sacks have been the measure of pass rushers for years but again, it’s only part of the whole story. Defensive end Ray Edwards of Minnesota managed just 6 sacks in 15 games but also weighed in with 14 hits and 33 pressures. The other piece of missing information is how many times he actually rushed the QB — 492 times, in this case. That’s a lot more pressure than the average DE from that many rushes.

On the other hand, Joey Porter of Miami rushed the passer 567 times and sacked the QB 17 times but managed only an additional 9 hits and 24 hurries. Porter gets notoriety from the sacks but an average 3-4 OLB, going after the quarterback as often as he does, should actually get more pressure.

In summary, sacks are a statistic that needs to be used with caution. When you hear it being used as evidence for anything other than the number of sacks given up or gained, you should be highly sceptical.

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