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The 49ers in 2009 by the numbers: Defense

While the 49ers 2009 offense was less than stellar (to put it kindly), the defense brought an intensity and level of performance we haven't seen in some time.  There were issues with consistency, but if you had to pick the best unit of the 3 (O, D, ST), the defense would get the nod.  As we look at the defensive stats, it's an interesting look.  As I mentioned in the Greg Manusky approval rating, the defense was a mix of bend-but-don't break and ball-hawking aggressiveness.  At times it was hard to tell if the defense was really that solid, but in the end the numbers show a very solid defense.

Total YPG
: 326.4 ypg (15th)
Passing YPG: 229.4 ypg (21st)
Rushing YPG: 97.0 (6th)
Points Per Game: 17.6 (4th)

Total Defensive DVOA: -12.3% (4th)
Passing DVOA: -11.1% (8th)
Rushing DVOA: -14.0% (6th)

The total yards and passing yards are certainly not particularly good.  There's your bend-but-don't-break in effect.  As we can see in points per game and the DVOA stats, the team was much better than the 15th ranking for total yards per game.  A perfect example might be the 49ers matchup with the Colts.  In that game Peyton Manning threw for 347 yards, but the defense was able to keep him out of the end zone, and keep the 49ers in a game most people figured would be a blow out.

We take a look at impact plays, defensive front seven performance, receiver coverage and drive stats after the jump...

"Impact" Plays
Sacks: 44 (t-3rd)
Tackles for loss: 48 (no rank)
Interceptions:18 (10th)
Fumbles Forced: 23 (no rank)
Fumbles Recovered: 15 (1st)

Calling this "impact" plays might not be a perfect title, but I look at these plays as the biggest impact plays a defense can make.  The fumble numbers might be a little fuzzy.  I went with ESPN's fumble count because has various fumble stats that aren't explained.  Either way, those are some impressive numbers.  I've often read there is a certain amount of luck involved in fumble recoveries, but I haven't seen the same thing with fumbles forced.  If that's the case and a team forces more fumbles than another team, wouldn't that increase their chances of recovering fumbles?  Maybe not, but it's still something to consider.

Defensive front seven Performance
Adjusted Line Yards: 3.68 (8th)
Power Success (Percentage of runs on third or fourth down, two yards or less to go, that achieved a first down or touchdown. Also includes runs on first-and-goal or second-and-goal from the two-yard line or closer.): 64% (16th)
Stuffed (Percentage of runs where the running back is tackled at or behind the line of scrimmage): 19% (16th)
2nd Level Yards (Yardage gained by running backs between five and 10 yards past the line of scrimmage, divided by total running back carries): 1.08 (8th)
Open Field Yards (Yardage gained by running backs at least 10 yards past the line of scrimmage, divided by total running back carries): .59 (9th)
Adjusted Sack Rate: 7.9% (3rd)

The 49ers were in the middle of the pack when it came to stuffing running backs, but a bit higher up in stopping teams at the second level and beyond.  I think that comes from having guys like Nate Clements early and Michael Lewis and Shawntae Spencer throughout the season.  Given that the 49ers lost Clements with a lot of time left in the season, this goes to show they've certainly got some solid tacklers elsewhere on the field.  It'd be nice to get some more stuffs though to ease the workload later.

Receiver assignments
vs. #1 WR: 4.9% (17); 9.3 pass attempts/game, 84.1 yards per game
vs. #2 WR: -34.0% (1st); 5.8 pass attempts/game, 34.4 yards per game
vs. Other WR: -18.3% (6th); 5.3 pass attempts/game, 36.6 yards per game
vs. TE: -13.3% (6th); 7.2 pass attempts/game, 49.6 yards per game
vs. RB: 15.8% (23rd); 7.6 pass attempts/game, 48.2 yards per game

One of my favorite features at Football Outsiders is there look at how a team's defense performs against specific receivers.  As this shows, the 49ers had a lot of success against teams' #2 wide receiver and tight end.  There is of course the question of who is the #1 WR and who is the #2 WR.  FO itself admits that their decision on who is what is a bit subjective.  I suppose for most teams you have a general idea of who is #1.  But then look at a team like New England.  Randy Moss is the game breaker and most talented of their receivers, finishing with 13 TD caches.  On the other hand, Wes Welker finished with the most receptions and the most yards.  Welker got the team down the field incrementally, and Moss blew up the defense.

For the 49ers, it becomes a bit more difficult with the in-season demotion of, and then injury to, Nate Clements.  Early on Clements would tend to cover the #1 guy, with Spencer covering the #2 guy.  When Clements went down, we saw Tarell Brown in the starting lineup, then Dre Bly.  Spencer was generally the #1 guy, but it still mixes up the performance above against #1 and #2 receivers.

Drive Stats
Yards/Drive: 24.79 (2nd)
Points/Drive: 1.33 (2nd)
TDs/Drive: .129 (2nd)
Punts/Drive: .470 (5th)
TOs/Drive: .158 (8th)
INTs/Drive: .089 (17th)
Fumbles/Drive: .069 (3rd)
LOS/Drive (Avg starting field position): 29.40 (17th)
Drive Success Rate (DSR - percentage of down series that result in a first down or touchdown): .612 (2nd)

These stats are interesting, but require context (as most any does).  Above we saw that the 49ers were 15th in total yards per game given up by their defense.  Here they're second in yards per drive.  Well, their offense was slightly less than stellar in moving the ball down the field, finishing 31st on offense in punts per drive (.508).  Given that number, the 49ers defense was dealing with a whole lot more drives each game than most teams.  Accordingly, the totals may be bad, but this is one more stat to show how solid the defense really was.  Even more impressive is the fact that they had to be getting worn down due to all the time on the field, and yet they still were 2nd in arguably the two most important categories (Yds/Dr and Pts/Dr).