So far this week I've reviewed the 49ers' overall and offensive stats for the 2008 season. Today, in the third, and final, part of my season review, I'm going to focus on defense and special teams performance.

The conventional wisdom about the 49ers' defense this past season is that Nolan's advocacy of a 3-4/4-3 hybrid base defense, and his affinity for the "Big Sub" (BS?) package, were obstacles to effective performance, and that Singletary's shift to a BS-lite, 3-4 defense led to defensive improvement later in the season. As has often been the case, the conventional wisdom is only half-right. Which half is right? Keep reading for the answer.

THE FLIP SIDE

Below is a table showing the 49ers' defensive performance this past season (Remember, positive percentages mean below average defense):

Compared to the offensive stats I presented yesterday, the Niners' defense was more efficient and more consistent. However, like the offense, the defense was actually worse towards the end of the season than it was during the beginning or middle of the season. As you'll see a little later, though, that's not to say that the defense wasn't improving at the end of the season. In terms of defense against specific types of plays, the run defense was considerably better than the pass defense.

Below is a graph that tracks total defense, pass defense, and rush defense DVOA from 2004-2008:

Unbeknownst to us, the defense seems to have gradually improved each year since the Nolan era began. Likewise, the run defense has been better than the pass defense every year. Why? Well, the reasons are coaching and personnel of course.

In 2004, the defense was that bad because of (a) a no-name DC (Willy Robinson), (b) the oft-injured Ahmed Plummer and the oft-burned Mike Rumph as starting CBs, and (c) Julian Peterson's Achilles injury. So in a sense, the only place to go was up in 2005. The hiring of Mike Nolan, a defense-minded head coach, helped the inevitable ascension as well. In 2006, the pass defense improved considerably thanks to the acquisition of Walt Harris and Mark Roman. Although they filled out their current secondary with Nate Clements and Michael Lewis in 2007, it was actually the run defense that improved thanks to the additions of Patrick Willis and Aubrayo Franklin. Finally, in 2008, acquiring the disruptive Justin Smith, combined with the "Big Sub" focus under Nolan, and the more prominent roles of Manny Lawson, Parys Haralson, Ray McDonald, and Roderick Green under Singletary, led to a further improvement in pass defense.

One last thing I'll say about the graph is that its upper limit is 0%. As was the case with the offense, the defense has been below average throughout the Nolan era.

After the jump, I'll break down the 49ers' defense DVOA, and evaluate specific players based on directional pass and run defense. I'll also review the special teams stats...

GROWING PAINS

Below is a graph tracking the 49ers' defense DVOA over the course of their 16 games:

Returning to what I said in the intro, it turns out that Nolan's hybrid and Big Sub defenses weren't actually that much of an impediment, if at all, to defensive success . Indeed, the only 3 above average games for the Niner defense in 2008 (vs. DET, vs. NE, @ NYG) occurred while Nolan was the head coach. In fact, I think it's pretty ironic that the 2^nd-best defensive performance of the season turned out to be a game that was the final nail in Nolan's coffin. I guess those JTO red zone picks, and all-around offensive ineptitude, didn't help Nolan's cause. Far be it from me, though, to blame Mike Martz or suggest that the offense sucked.

The 2^nd part of conventional wisdom was also correct. It does seem that Singletary's simplification of the defense, through an exclusive 3-4 identity and a reduction in Big Sub, helped get the defense back on track after a couple of weeks of adjustment. Indeed, when you combine this graph with its offensive counterpart in Part 2, the evidence seems clear that there was an overall adjustment period when Singletary took over. Perhaps that's why he kept saying, "Just keep watching," as they kept losing those first few weeks.

More evidence of the idea that Nolan's defense wasn't as bad as it seemed comes from the following table:

Supplementing the stats in the previous graph, the defense seems to have been considerably better under Nolan than it was under Singletary. Of course, we have to take into account two things here. First, Week 10, which is included in Singletary's stats, was the "Leonard Weaver contract push" game vs. SEA, for which the new head coach only had a few days to prepare. Second, as I alluded to above, Weeks 10-17 also included that Singletary adjustment period. Nevertheless, the stats in this table are hard to argue with.

BEND BUT DON'T BREAK...SOMETIMES

Below is a table showing the 2008 49ers' defense DVOA in each of 5 field zones:

These stats seem to give us an evaluation of the Niners' bend-but-don't-break defensive philosophy. Under normal drive starting conditions (i.e., OPP 20-39), the defense allowed other teams to warp zone across midfield. Inside the SF 40, however, the defense clamped down, albeit with mixed results. They were in the top half of the league from the SF 39-20, and in the 3^rd quartile if opponents entered the red zone.

Here's some more detail about what happened once opponents entered the SF red zone:

At first glance, it's obvious that rush defense was the main culprit in the Niners' red zone mediocrity. However, looking at this in more detail, there appears to be a relationship between the pass vs. rush numbers in this table and the red zone vs. goal-to-go numbers in the previous table. Specifically, because opponents are more likely to run the ball inside the 10, the impact of a bad rush defense DVOA was magnified, leading to a higher overall defensive goal-to-go DVOA. Similarly, an increased likelihood of opponent passes from the SF 20-11 magnified the impact of good pass defense DVOA on red zone performance overall.

#5: FINISH

Below is a table showing the 2008 49ers' defense DVOA by quarter and half:

Two main conclusions can be drawn from this table. First, we've identified which units were the culprits for the 49ers overall ineptitude in the 2^nd and 3^rd quarters. Looking back at the total DVOA stats in Part 1, most of the 2^nd quarter total (-32.5%, 30^th) was the defense's fault, whereas most of the 3^rd quarter total (-31.6%, 28^th) was the offense's fault. Looking back at the 49ers' schedule, this makes sense. In games vs. ARI, @ NO, vs. NE, @ DAL, @ STL, and vs. WAS, the Niners' defense turned a lead at the end of the 1^st quarter into a tie or deficit at halftime. The second conclusion is that the Niners' defense did their part when it came to the 5^th factor in Singletary's Formula for Success, finishing: They were top 10 in both 4^th quarter DVOA and late/close DVOA. Again, this makes sense. Looking at the schedule, the defense gave up fewer than seven 4^th-quarter points 9 times, 5 of which came in their final 6 games under Singletary. In fact, they had a 5-game streak (Weeks 12-16) in which they allowed fewer than 7 points during the 4^th quarter of each game.

WORSE WHEN WINNING?

Below is a table showing the 2008 49ers' defense DVOA by score gap:

Overall, the stats show that the Niners' defense performed pretty much the same whether they were winning or losing. However, if you compare the DVOAs and rankings instead of the DVOAs themselves, the conclusion becomes a little more nuanced. According to DVOA, the Niners' defense was, in fact, worse when winning. However, if you look at their standing amongst the 32 NFL teams, they were actually in the top half of the league in defense DVOA when winning.

What's going on here? Basically, this discrepancy occurred because the average NFL defense is more efficient when it's behind than when it's ahead. When you take the stats out of it, this makes perfect sense because opposing offenses tend to dial down their aggressiveness while ahead. This relates to the Niners' stats in the following way. The 49ers were actually worse than most other NFL defenses while losing, despite the fact that they were better as a team while losing. Analogously, the 49ers were actually better than most of the other NFL defenses while winning, despite the fact that they were worse as a team while winning (Aside: That sentence went through about 10 iterations before I came up with what I thought was the least confusing way to articulate the point. I'm still not sure I succeeded. If not, let me know and I'll take another stab in the comments section.).  All in all, though, I'll take the conservative route and just conclude that there wasn't much of a meaningful difference on defense between being ahead and being behind.

HOME, SWEET HOME

Below is a table showing the 2008 49ers' defense DVOA by game location:

This table is a lot like the last one. Overall, the 49ers' defense played twice as poorly on the road as they did at home. However, once again, the better DVOA is associated with the worse ranking because the average NFL defense is more efficient at home than on the road. I guess the moral of the story is this: The defense needs to improve both at home and on the road. But in trying to assign blame for the 49ers' overall road woes, you'd have to fault the offense (-23.6% road DVOA, 32^nd) more than the defense.

A GAME OF 36 INCHES

Below is a table showing the 2008 49ers' defense DVOA under different down and distance situations:

For the 2008 49ers' defense, it really was a game of inches. To be exact, it was a game of about 36 inches. They were 40.2% more efficient on 2^nd and long than they were on 2^nd and mid, whereas they were 118.7% less efficient on 3^rd and long than they were on 3^rd and mid. To be honest, this one's hard to explain. The only thing I can think of (as of right now) is a problem with their nickel and/or dime packages. The reason I say this is because, when faced with 2^nd and 4-6 yards, opposing offenses are still likely to run the ball a decent percentage of the time, and therefore, the Niners' defense is less likely to be in nickel or dime. The opposite seems true on 3^rd and long. The opposing offense is almost always going to pass, so the Niners are almost always going to be in a pass defense with extra DBs. Feel free to comment with your own thoughts on this though.

In at least one respect, the following table showing offense DVOA by type of play supports my hypothesis:

The way I see it, the 49ers' pass defense was considerably worse on 3^rd down than its run defense, thereby inflating the 3^rd and long stats. In contrast, the 49ers run and pass defenses were equally bad on 2^nd down, thereby combining to produce a bad 2^nd and mid stat. I'm not sure about this 2^nd part, but it's all I can figure at the moment. 

THE PLAYER'S CLUB - DEFENSIVE FRONT 7

Obviously, due to changes in personnel, positioning, and play design, the defensive line is harder to evaluate using ALY (and directional ALY) than is the offensive line. For this reason, the preferred interpretation for defensive ALY is actually the adjusted yards per carry allowed by the defensive front 7. Despite these situational changes, the general tendency is for certain members of the front 7 to be in on all downs (e.g., Willis), certain members to only be in on running downs (e.g., Lawson and Spikes), and certain members to have designated responsibilities (e.g., Franklin two-gapping, and Willis finding the ball carrier). Therefore, using ALY is not an altogether futile exercise. At the very least, it's better than using the NFL's stats, which don't account for opponents or game situations.

Here are the 49ers' front 7 stats for 2008:

As I presented earlier, the 49ers' run defense was just about average in efficiency, and ranked 18^th among the 32 teams. The stats in this table seem to suggest that, not surprisingly, their overall run defending performance was mostly attributable to the front 7: Their ALY was 12^th-best in the league, and they allowed the 9^th-fewest percentage of yards beyond the first 10 yards of a run. The front 7 still had serious weaknesses though. They were in the bottom half of the league in both power running defense and the percentage of opponent carries that they stopped for negative yardage. Most concerning, though, was their ASR. It's probably not news to you that the Niners lack a pass rush. It probably is news to you that their ASR was worse than their actual sack rate (5.2%), meaning that their sacks in 2008 were easier than the league average in terms of opponent, down, and distance.

In terms of directional running performance, below is a diagram showing how well the front 7 executed, and what percentage of running plays were called against them, in each direction:

Supporting the opinions of others, Franklin had a good year stopping runs up the middle. Well, let me rephrase. Franklin had a good year eating up blockers so that Willis could stop runs up the middle. In addition, these stats show why Manny Lawson, when healthy, plays primarily on run downs: He's pretty good in run support. Justin Smith's performance is a little difficult to judge because he spent half of the year bouncing around between RDE and LDE. Although, Maiocco did point out that his high motor and aggressiveness have a tendency to take him out of plays from time to time. Either way, opponents' runs behind tackle, regardless of direction, met little resistance from the Niners' DEs. Finally, it looks like Parys Haralson needs to improve his run-stopping skills. Taken together, then, the 49ers could use some improvement at DE, and perhaps a run-stopping LOLB to let Haralson focus on sacking the QB.

THE PLAYER'S CLUB - DEFENSIVE BACK 7 (OR 8)

The last set of stats I'll present about the defense concern their performance against an opponent's receivers, whether they are WRs, TEs, or RBs. The same situational limitations of ALY for evaluating the front 7 apply with respect to using DVOA to evaluate DBs: Personnel, positioning, and play design are not the same on every play. Nevertheless, considering that DVOA is the best stat currently available to the public for these purposes, and that I've attempted to accurately display the 49ers' nickel and dime personnel and positioning, it remains a worthwhile endeavor.

Most of the time in nickel, the Niners brought Tarell Brown in to replace Manny Lawson, and moved Walt Harris inside to cover the slot receiver. Most of the time in dime (that's a rhyme...wait...that rhymes too), the Niners used Donald Strickland - or Dashon Goldson, when healthy - as a 3^rd safety in place of Takeo Spikes. Otherwise, the rest of the main pass defense positions stayed the same a majority of the time. Below is a diagram displaying the relevant stats:

These stats lead to a couple of interesting conclusions. First, Nate Clements sure did get a lot of passes thrown his way for a so-called "shutdown corner." Second, depending on whether the Niners are in their base or nickel defense, they did a better job covering the opponent's #2 WR than Nate Clements did covering the #1. Third, either Harris needs to be moved out of the slot in nickel, or Mark Roman needs to do a better job helping down the field (See David Martin TD @ MIA). Take your pick. Fourth, I wonder if the fact that opponents attempted a disproportionate number of passes to RBs was a byproduct of the 49ers' bend-but-don't-break pass defense philosophy. Fifth, the LBs did a good job covering all those passes intended for RBs. Finally, Michael Lewis was mediocre in pass coverage against TEs.

SPECIAL TEAMS

The rest of this article will focus on the special teams. You can find the detailed methods used to calculate special teams DVOA here. Just as an introduction, I'll give you the short(er) version. Basically, unlike offense and defense DVOA, for which they define efficiency as gaining or preventing an adequate number of yards towards a first down on a given play (after adjusting for opponent and game situation), Football Outsiders defines special teams efficiency as providing a net advantage to the team via starting field position and FG distance. Their method is based on the fact that each yard line is associated with a different league-wide likelihood of scoring points on a drive or FG attempt. This is pretty intuitive: It's much easier for the average team to score on a drive starting at the opponent's 40 than it is starting at their own 10, and it's much easier for the average kicker to make a 30-yard FG than it is to make a 50-yard FG

So, special teams DVOA (a) converts a team's kick distances (for FGs and extra points) and kick-related changes in field position (for kickoff coverage, punt coverage, kick returns, and punt returns) into expected points, (b) subtracts the team's adjusted expected points from its opponent's expected points to get a net expected points value, and (c) adjusts that net expected points value to account for weather and altitude. Obviously, a special teams unit wants to give their team a net advantage in expected points, so positive DVOA numbers mean higher efficiency.

Below is a table showing the 49ers' special teams performance this past season:

As you can see, the Niners' special teams was one of the best in the league. Although all 5 special teams were top 10 in the league, kickoff coverage stood out, giving the 49ers an advantage of almost 10 likely points over their opponents.

I have three other things to say here. First, the acquisition of Allen Rossum was more beneficial for kick returns than it was for punt returns. Although I'm not presenting a graph here, net punt return points with Michael "Beer Man" Lewis at punt returner last year was nearly 3 times better (3.46), whereas net kick return points last year was almost 8 points worse (-1.48). Second, because I'm not going to display the special teams 2004-2008 graph - believe me, it's pretty boring - trust me when I tell you the 49ers' special teams have been on a steady upward trajectory for 5 seasons now. Finally, taken together, these stats mean that the kickoff and punt teams (coverage and return) gave the Niners a 3-TD advantage in field position over their opponents. If only the offense and defense could have taken advantage of that -wait for it - advantage, this team "coulda been a contender!" Well, at least a playoff contender!

The final thing I'll present is the special teams' week-to-week performance in 2008. Here's the graph:

As you can see, in contrast to the offense and defense, the 49ers' special teams had 11 above-average games this past season. The highlight, for sure, was the Monday Night game @ ARI, in which Rossum returned the opening kickoff for a TD. In terms of the trendline, it was an up and down year - mostly up - with great performance in the middle of the season bookended by average or lousy performance at the beginning and end of the season.

BOTTOM LINE

To recap, we can draw the following conclusions from the defense and special teams stats I've presented here:

•The best word to describe the 49ers' defense this season is "mediocre." They were in the middle of the pack overall, against the run, and against the pass.

•Over the past 5 seasons, defensive acquisitions have had a demonstrable effect on performance.

•Nolan's "hybrid +Big Sub" defense and Singletary's "3-4 ‘til I die" defense were equally efficient when you take into account the adjustment period immediately after Singletary was promoted.

•Consistent with a bend-but-don't-break philosophy, the 49ers' pass defense, although mediocre overall, stiffened in the red zone. The opposite was true of the run defense.

•The Niner defense finished games well, especially under Singletary.

•Unlike the Niner offense, the Niner defense didn't fall apart on the road.

•The Niner defense was great on 2^nd and long, but horrific on 3^rd and long.

•Although good overall against the run, the Niners' front 7 needs to improve strength-wise because they gave up too many first downs on 3^rd and short, and didn't stop enough plays behind the line of scrimmage.

•The Niners need to improve on the edge because their DEs and OLBs (except Lawson) had a hard time stopping the run, and their pass rush was horrible.

•Opponents don't treat Nate Clements like a shutdown CB. Perhaps the 49ers also shouldn't.

•Both starting safeties seem expendable given their relative mediocrity in pass coverage this season.

•Tarell Brown looks like he has a future in the NFL.

•The 49ers are set on special teams. However, Allen Rossum was a much better kick returner than punt returner this season.

OK...that's it for the season review. Hope you enjoyed it, or at least learned something about this past season from it. Stay tuned the next couple of weeks for a stat-based look at available free agents who play positions that the 49ers need to upgrade.

**DVOA, ALY, and ASR statistics used to produce this article were obtained from Football Outsiders.