The 49er defense has been an enigma this season. This is the unit that kept Peyton Manning from throwing a touchdown...but gave them out to Matt Ryan and company like candy to trick-or treaters on Halloween. This unit surrendered an all time Candlestick Park worst 45 points to the Atlanta Falcons...and collected 5 interceptions from Jay Cutler just 4 games later. This unit started lights out, and for the most part, has been the best unit on the team for the duration of the season. With the exception the loss of the against Atlanta, the San Francisco defense has been good enough to keep the team in a position to win games...no easy task when one considers that the 49er offense was converting on less than 30% of its third downs before Alex Smith took the reins.

In part two of my three-part look back at the first half of the season, I'll be looking at the defense to determine what's gone right, what's gone wrong, what's getting better and what fans can expect to see going forward.

D-line steps up

There have been some real bright spots for the 49ers defense this season, and with the exception of Patrick Willis, the brightest thus far have to be the play of d-line starters Justin Smith and Aubrayo Franklin. The 49ers rank 3rd against the run, and have given up 100 yards to an individual rusher just once this season. Smith has been a force off the edge, and though he's only accounted for 1 sack and a forced fumble, he leads the all 49er D-linemen with 32 tackles. Despite fighting through double teams on almost every play, he is a nearly constant presence in the backfield of opposing offenses. Franklin has been equally dominant, having had a full offseason to absorb DC Manusky's simplified 1-gap 3-4 attack. His ability to shed blocks has led to a very productive season thus far, netting him 24 tackles and 2 sacks. Franklin's quickness off of the snap has kept runners in check between the tackles, commanded double team blocking assignments on almost every play and has done wonders for the play of the team's linebacking corps. While depth on the line isn't an issue, the performance of the players that comprise that depth is an issue. Ray McDonald has been dynamite as a third down pass rusher, and Isaac Sopoaga has been a quality backup thus far, but reserves Kentwan Balmer and Demetric Evans have been largely invisible thus far.

Tackles in spades...but where are the sacks?

The inside linebackers have been particularly effective, having collected 130 tackles, 3.5 sacks, 3 forced fumbles and 2 interceptions between them. Spikes has been slowed a bit by injuries of late, but Willis is enjoying the finest season of his career to date, and could be a candidate for Defensive Player of the Year if he finishes the season as well as he started it.

The 49er linebackers have been really productive this season, but haven't produced the one thing that 49er fans have been looking for over the past few seasons: sacks. In the DC Greg Manusky's 3-4 scheme, OLBs are relied upon to bring primary pressure on the quarterback, and to date, the results have been disappointing...between them, starting OLBs Manny Lawson and Parys Haralson have only 3.5 sacks. For this defense to be the lights out, game stopping unit it could be, Lawson and Haralson will need to step it up...big time. Expectations for Haralson were huge coming into this season, especially considering that he earned his 8 sacks last season in 9 starts. Lawson has been getting pressures and hits on opposing quarterbacks, but seems to be a step slow off the snap. Both Haralson and Lawson have excelled at setting the edge, but neither has been able to generate the kind of pressure necessary in a 3-4 attack...and of that doesn't change over the next 7 games, look for the 49ers to address the pass rush in the offseason.

Speaking of the secondary

At the start of the season, the secondary was of primary concern, and with good reason. Starting cornerback Walt Harris had been sidelined for the year, and the team acquired Dre' Bly to replace him. Mark Roman had been replaced by first time starter Dashon Goldson, and questions loomed about backups Shawntae Spencer and Tarell Brown. The 49ers have been vulnerable through the air in recent seasons, and many expected this unit to be the Achilles' heel of the defense.

After 9 games, early season concerns are gone...but new concerns have arisen. Nate Clements' severe shoulder injury may have ended his season, and though his replacement Tarell Brown has performed admirably in relief, the loss of Clements leaves the secondary extremely challenged in terms of depth. Goldson has performed well to date (55 tackles, 1 ff, 1 sack and 2 int), but his aggressiveness has left him susceptible to being exposed on deep routes. Mike Lewis has played well when healthy, but his long term viability is questionable, as he has been sidelined with 3 concussions this season.

Injuries and substitutions aside, this unit is surrendering 248 yards per game...which ranks them 28th in the league. If they're going to get healthy, the next seven games would be the time to do it. Of the remaining teams on their schedule, only the Cardinals and the Eagles, ranked 5th and 9th respectively, are among the top ten in passing offense. The 11th ranked Packers are prolific at piling up yards, but they are also prolific at giving up sacks. Provided that the pass rush steps things up, a modest improvement in pass defense isn't out of the question.

Will it get better? When?

So, is this defense better than its 18th overall ranking? The short answer is...yes. The team is surrendering 20 points per game...good enough for 11th in the league, so though they may be giving up a lot of yards through the air, the team is still relatively stingy in the red zone. For the defense to truly take their performance to the next level, only one piece of the puzzle is missing: the pass rush. Over the next few games (especially against the Packers), look for Greg Manusky to tinker with blitzes and stunts up front to get more pressure on opposing passers. This should give the pass defense a break, generate turnovers, and net the team some sacks...but if you are looking for an epiphany of "1985 Chicago Bears" proportions, prepare to be disappointed. This defense is good, but until the 49ers add a bonafide, shop wrecking pass rusher they simply don't have the tools to be great.