How important ARE sacks?

Since the football season is still another 2 or so days, I wanted to write this analysis before the Superbowl. We all know how glorified sacks are, but in the end, they're basically just negative running plays. But do they inflict some kind of psychological damage on the opponent?

I looked at the 2006 16 game schedules for 3 teams: the Gmen, Pats and Raiders. Examining every game's play-by-play (thanks NFL.com) for when sacks occurred, and what the outcome of each drive was, I compared the data to the average 2006 NFL drive.

- Sacks occurred in 18.7% of all drives (roughly 1 in 5).

- The most likely result of a drive after a sack occurred was a punt: 55.2% of the time. This is 16.1% higher than punting on an average drive: 39.1%. This is expected.

- Turnovers actually occurred less frequently after a sack: 20%. Compared to an average drive which produced a turnover 21.3%. The difference is slight, but I did not expect to find this. It must mean that offenses get conservative after a sack. Teams will take more chances on 3rd & 5 than on 3rd & 15.

- When a sack occurred, the offense failed (to score a TD or attempt a FG) 75.2% of the time. That's 14.8% higher than on an average drive.

- A TD or FG attempt occurred on an average drive 32.2% of the time. But when a sack occurred, it dropped to 13.8%. A big 18.4% difference.

- A TD was scored on an average drive 16.9% of the time. That dropped to just 2.9% on drives after a sack occurred. So basically, if a sack occurs, the offense can basically forget about scoring a TD. It happened just once out of every 34 drives with sacks!

Avg. drive
D holds (forces a punt or turnover) 60.4%
D fails (allows a TD or FG attempt) 32.2%

'Sack' drive
D holds 75.2%
D fails 13.8%

75.2-60.4=14.8
32.2-13.8=18.4
+
33.2

- So adding the percentages that the defense will get the ball back (either through a punt or a turnover), or minus the 'scoring chances' (TD or FG attempt), I'm left with: the D will hold (or the offense will fail) 33.2% more often after a sack than an average drive. In other terms, 2.2 times more often (61.4/28.2=2.2).

Do sacks equal wins?
The top 10 teams in sacks 2006 (with their overall D ranking):
SD, #10 overall defense
Baltimore, #1
Miami, #4
GB, #12
NE, #6
Seattle, #19
Car, #7
Buffalo, #18
Philly, #15
Chi, #5

Avg. ranking of #10. Only 4 of these teams missed the playoffs.

The bottom 10 teams:
Wash, #31 overall defense
TB, #17
Indy, #21
Tennessee, #32
Houston, #24
Cleveland, #27
Min, #8
Det, #28
KC, #16
NYG, #25

Avg. ranking of #23. Only 3 of these teams made the playoffs.

Obviously, sacks are a very large component to overall defense. Howevever, sacks are not the only determinant to defense, as Minnesota was among the last in sacks, yet ranked 8th in overall defense. Miami and Carolina had a lot of sacks and good defenses, but their offenses were not good enough to make the playoffs. The Colts, who were 2nd to last in sacks (and 21st in defense) are in the Super Bowl.

If you'd like the raw data, just let me know.