The 49ers had one of the best pass defenses in the NFL last season during the regular season. But things got a lot more difficult in the two playoff games and Super Bowl.
The passer rating for opposing quarterbacks against the 49ers was just 78.0 in the regular season. In 16 games, the opposition averaged just 6.1 yards per attempt with 19 touchdowns and 14 interceptions.
In the three postseason games, Aaron Rodgers, Matt Ryan and Joe Flacco combined for a 109.5 passer rating against the 49ers and an 8.2-yard average per attempt with eight touchdowns and two interceptions.
The only cornerback the 49ers have made much of an effort to acquire this offseason is Nnamdi Asomugha. The 49ers are awaiting word from Asomugha, who has also attracted attention from the New Orleans Saints after the Philadelphia Eagles cut him.
If Asomugha (6-foot-2, 210) signs with the 49ers, he would not be guaranteed anything. After all, he turns 32 in July and is coming off two miserable seasons with the Eagles. He would likely be put into more press-coverage situations, which would seemingly give him a better chance to succeed. But it's also entirely possible Asomugha is not as good as the cornerbacks already on the 49ers' roster. That's why the 49ers guaranteed Asomugha nothing more than a chance to compete for playing time.
Many who watched Asomugha on a weekly basis in Philadelphia the past two seasons believe he no longer runs well enough to be effective. According to Pro Football Focus, opposing quarterbacks had a 120.6 passer rating when targeting Asomugha last season with 66.7-percent completions, five touchdowns allowed and one interception.
Asomugha would face stiff competition to get onto the field if he signed with the 49ers. The same goes for any player the 49ers might select in the draft.
Carlos Rogers (6-0, 192): He is one year removed from being named to the NFC Pro Bowl team. Rogers (6-foot), like Asomugha, turns 32 in July. He played left cornerback on base downs and then moved inside to the slot in passing situations. The opposition completed 70.1 percent of its passes against Rogers last season. He gave up three touchdowns with one interception. The opposition's passer rating against him was 92.9. Two sources told CSNBayArea.com that the 49ers are committed to Rogers for another season. He is scheduled to earn $5.85 million in 2013.
Tarell Brown (5-10, 193): He is 28, and played very well in his second season as a starter. The opposition managed just a 75.2 passer rating against him. He did not allow any touchdowns, according to Pro Football Focus, with two interceptions. Only 58.9 percent of the passes thrown his way were completed. His contract expires after the 2013 season, and he figures to be in line for a nice next contract.
Chris Culliver (6-0, 200): He turns 25 in August, so he figures to be around for a while. Culliver came in when the 49ers went with extra defensive backs. He played 63.2 percent of the time, mostly at left cornerback. The opposition completed just 49.3 percent of the passes thrown his way for a passer rating of just 76.9. He surrendered four touchdowns and had two interceptions. Of course, he struggled in the 49ers' 34-31 loss to the Baltimore Ravens in the Super Bowl.
The 49ers also are in line to return their fourth and fifth cornerbacks from a year ago. Perrish Cox is under contract, and the 49ers tendered restricted free agent Tramaine Brock for one year at $1.323 million.