49ers Midseason Grades: Defense

The 49ers' defense got off to a rough start, allowing 28 points per game during the first three weeks. It's no accident the defense has tightened over the last five games coinciding with the team's lop-sided five-game winning streak. Inside we'll offer grades, position by position, for San Francisco's talented defensive unit.

Things didn't start very well for the San Francisco 49ers' defense in training camp. They lost Patrick Willis with a broken hand and Chris Culliver for the season with a torn ACL. They also re-tooled at safety and the defensive line, acclimating rookie Eric Reid, first-year starter Ian Williams and free agent Glenn Dorsey to the team.

That adversity was apparent over the first three weeks of the regular season, as defense struggled to contain the Packers, Seahawks and Colts. The team went 1-2 to start and authored the first losing streak since Jim Harbaugh took over in 2011.

The struggles weren't limited to the defense, of course. The offense attempted a reformation with considerable turnover of outside weapons in the passing game. But when the 49ers went to St. Louis as a desperate team on Thursday night in Week 4, they returned to their Super Bowl form. That night San Francisco ran for a season-high 219 yards while allowing just 188 total yards to the Rams. Since then, the 49ers have been what many expected them to be coming into the season as defending NFC Champions.

During the team's five game winning streak, all by double digits, San Francisco's defense has averaged 12.2 points allowed. For the year, the Chiefs lead the league with 12.3.

To be fair, the 49ers haven't played a good offensive team since the Colts beat them 27-7 in Week 3. But they haven't slipped against their inferior opponents either.

Safeties: B+

It's hard to argue with Eric Reid and Donte Whitner have done this season. The duo has molded together seamlessly after the departure of All-Pro Dashon Goldon.

Reid has been consistently solid since taking Goldon's place at free safety. He started his NFL career with interceptions in his first two games and is tied with Tramaine Brock for the team lead with three.

The biggest difference between Reid and Goldson is his ability to tackle legally. Goldson became one of the biggest hitters in the league at his position, but he made a habit of leading with his head, making him an easy target for personal-foul penalties. Reid's tackling is predicated on his ability to wrap up using his long arms. But he runs into trouble when he takes sharp angles to the ball carrier in open space. Through eight games, Reid leads the team with nine missed tackles according to Pro Football Focus.

Whitner is having one of the best seasons of his career. And it's no surprise it's coming with his free agency looming at the end of the season. The eight-year vet might be the team's toughest decision come spring. Given the way the team replaced Goldson with Reid in the draft, the team could go the cheap route and draft another safety early on. Otherwise, the team could use some of its cap space to lure a free agent.

But after allowing 12 touchdowns in coverage last season, including two in the Super Bowl loss to the Ravens, Whitner has shown drastic improvement so far in 2013. He has yet to allow a score in coverage and quarterbacks have a 47.5 rating when targeting his man. His diving interception against the Rams after Brock's deflection might be the highlight of the season for the defense. And the play he made forcing Jermichael Finley out of bounds and preventing him from making a catch in Week 1 was vital in preserving the 34-28 win.

Corner: B-

It's been a mixed bag for the 49ers' corners so far this season. There has been solid play, highlighted by Brock's two-interception performance against the Texans, and there have been some plays the team would like to have back.

Nnamdi Asomugha played well in pass coverage in his three games with the team before being released recently, but missed some important tackles in the open field. Brock's play, paired with Asomugha's inability to play on special teams, led to the veteran's release.

At 32, Carlos Rogers put together a solid year considering his difficult assignment each week of covering the opposition's slot receiver. Overall, quarterbacks are completing just 50 percent of their passes when targeting his man. But Rogers struggled in Week 1 against Randall Cobb, allowing three receptions on three targets and a touchdown. He also struggled to defend Kendall Wright of the Titans in Week 7.

Brock has played very well since taking over for Asomugha as the team's nickel corner. But he's also allowed touchdowns in three-straight games. He's made a habit of gambling to make the big play and at times those gambles have not paid off.

Tarell Brown has been both good and bad in the season's first half. His best game came against Houston, when he allowed just two receptions on seven targets, including two of five while covering Andre Johnson. But for the season, quarterbacks have completed 25 of 44 throws on Brown for a pair of touchdowns and a 96.4 quarterback rating.

Overall, the corners have played well enough to maintain a top-10 passing defense in the NFL. But there hasn't been standout play from any one player on a consistent basis. They have played well enough against poor offenses, but we will know more when they face Carolina and New Orleans over the next two weeks.

Brown and Brock are both in the final years of their respective deals. And Rogers is due over $6 million next season. Given the way they've played so far, it looks like there could be a lot of turnover at cornerback in 2014.

Inside Linebackers: A-

There might not have been any more impressive performance from a 49ers defender than what NaVorro Bowman did against the Rams in Week 4 when the team needed a win in the worst way. He came up with two sacks, two quarterback hits, three hurries and made five stops while the defense held St. Louis to 188 yards in its own building.

The reasoning for this high grade comes largely because of Bowman's outstanding play while Patrick Willis has either been absent or dealing with his injury. Willis came into the season having missed most of training camp and all of the preseason while recovering from his broken hand. Later, he suffered his groin injury in the second half of Week 3's loss to the Colts and went on to miss the next two games. This grade would have been an A had the linebackers played better during the second half of the loss to Indianapolis.

Willis hasn't been himself because of the groin injury, but is still second on the team in tackles despite playing in just six games. Willis' best game of the first half came against the Jaguars, which bodes well for his second half after the bye week.

Despite coming into the season with just a handful of defensive snaps under his belt, Michael Wilhoite played well in Willis' absence. He benefitted greatly from taking most of the All-Pro's reps during training camp and playing the majority of all four preseason games. His experience gained during that time will be invaluable should either Willis or Bowman have to miss any time later on.

Outside Linebackers: B+

Through three games before his leave of absence, Aldon Smith racked up five sacks. In his stead, Corey Lemonier and Dan Skuta filled in admirably, but the sack totals weren't there. The duo that alternates according to the situation combined for just one sack: Lemonier's safety against the Cardinals, which was the first sack of his career.

Despite having just one sack, the rookie pass rusher played very well given the circumstances. He generated 18 quarterback pressures in his six games and became a player offensive lines need to be aware of.

Skuta was having a relatively non-descript season while filling in for Smith, which is both positive and negative. He's stood up against the run without being exposed in the passing game, but the team would like him to get to the quarterback more consistently. As he continues to transition from inside linebacker to the outside, pass rushing is where Skuta can improve his game the most. His fumble return for a touchdown against the Jaguars was one of his few standout plays of the season.

Perhaps the defense's most undervalued player, Ahmad Brooks, is having another outstanding season. The soft-spoken strong-side linebacker continues to play well next to the team's terrific defensive line and inside linebackers. His four sacks rank second on the team behind Aldon Smith and he continues to grade very solidly against the run each week. So far, it appears Brooks is backing up his Second-Team All-Pro selection from last season. And no 49er is more adept to batting down passes at the line scrimmage.

Defensive Line: B+

All four of the defensive linemen atop the depth chart have dealt with injuries of varying degrees in the first half of the season. The worst was Ian Williams' broken ankle that cost him the year. Ray McDonald has played through a biceps injury that zapped the strength from his right arm that might never get back to 100 percent this season. Justin Smith has had a lingering shoulder injury that hasn't taken away from his typical high level of productivity. And newcomer Glenn Dorsey has spent the last few weeks dealing with a hamstring injury that caused him to leave Week 6's win over Arizona early.

With those injuries in mind, it's a minor miracle the team's defensive line has played so well.

Since coming over as a free agent in the offseason, Dorsey has been very good in base situations against the run. The Chiefs' former first-round pick in 2008 has taken very well to Jim Tomsula's coaching and has been an upgrade over the departed Isaac Sopoaga and Ricky Jean-Francois.

While the starters have missed more time than normal while the team attempts to keep them fresh, Tony Jerod-Eddie and Demarcus Dobbs have gotten more time than reserves at that position have in the past. The two former undrafted players have held their own in their combined 115 snaps while giving Justin Smith and McDonald some much-needed breathers.

For Smith and McDonald, it's been more of the same as they continue to be one of the most solid 3-4 defensive end combos in football. Look for their production rise and snaps drop as the team works in rookies Tank Carradine and Quinton Dial in the second half of the regular season.

Defensive MVP: NaVorro Bowman

This choice was pretty clear. Bowman continues to improve in his fourth season while coming off back-to-back All-Pro selections. He took over the leadership role of the defense while Willis was out and continued to pick up the slack with Willis at less than 100 percent while dealing with his groin injury. Bowman's improved as a blitzer, becoming even more well rounded than he was before. With Willis able to get healthy during the bye week, expect a big second half from the team's inside linebackers.

*Statistics from Pro Football Focus were used in this report*

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