After yet another quarterback enjoyed a 300-yard passing game against the 49ers, coach Mike Singletary indicated that changes were in store for the defense.

Expect cornerback Dre Bly to replace Tarell Brown as a starter this weekend. Singletary held back on making it official Wednesday, but he indicated he needs to do something for a passing defense ranked 30th in the NFL heading into the 49ers’ game against the Jacksonville Jaguars on Sunday at Candlestick Park.
Singletary said the 49ers’ big problems are the little details.
“If you’re not exactly where you need to be, then it’s going to catch you at times, and that’s where we are,” he said. “We’re all about being exact, being exactly where we need to be. Our margin for error is very small. That’s where we are.”
Green Bay’s Aaron Rodgers threw for 344 yards last week, continuing an onslaught since Week 3 that has included Minnesota’s Brett Favre (301 yards), Atlanta’s Matt Ryan (329), Indianapolis’ Peyton Manning (347) and Chicago’s Jay Cutler (307).
To put it another way, the 49ers have allowed a 300-yard passer in half their games; they are 1-4 in those games.
Bly noted that several opponents piled up huge yardage on screen passes, which is to say that not all of the passing totals can be blamed on the secondary. But some of them can. Packers receiver Greg Jennings slipped past Brown, safety Dashon Goldson and safety Mark Roman on Sunday for a 64-yard catch-and-run.
Brown also missed a tackle on Jordy Nelson’s 7-yard touchdown grab.
After taking over the starting job in Week 7, Brown realizes he might be giving it back in Week 11.
“Coach will have the final say, and I’ll have to run with it,” he said. “At the end of the day, I just want to win.”
When Singletary has talked about the 49ers’ recent struggles, he often has noted their problems with the details. After the loss to the Packers, for example, he said the 49ers needed to “mature.”
Enter Bly, an 11-year veteran whose 35 interceptions since 2001 lead all defensive players during that span. He should have two more. Bly dropped an interception that could have sealed a victory against Minnesota, and he dropped another that might have turned the tide against Indianapolis.
“We’ve had the opportunities to make plays, and we’re not making them,” Bly said.
Maybe returning to a starting role will help. Bly said he has expected to be the starter since signing as a free agent in May.
The Jaguars run most of their offense through star running back Maurice Jones-Drew, who leads the NFL with 13 touchdowns. But the 49ers respect Jacksonville’s passing game, too. Mike Sims-Walker has at least 80 receiving yards in six of his past eight games. He leads the team with eight receptions of 25-plus yards.
And there is Bly’s friend, wide receiver Torry Holt. The two have known each other they were college stars in the Atlantic Coast Conference. Holt went to North Carolina State; Bly went to North Carolina.
“We used to hate each other,” Bly said.
Now the former St. Louis Rams teammates are so close that they go on vacations together. Their wives are best friends, too. The 49ers, however, cannot afford to let another receiver enjoy a day at the beach. Their offense ranks 27th in the NFL and is not designed to keep pace with the video-game totals being put up by recent opponents.
The 49ers’ defense was supposed to be the strength of the team. Linebacker Patrick Willis predicted that he would lead a top-five defense. Instead, the 49ers rank 22nd.
Part of the problem is the workload — the 49ers’ offense leads the NFL in three-and-outs — but fatigue can’t be blamed for all the defensive woes. The 49ers are giving up far more points in the first half (130) than the second half (80).
“We just have to continue to work better together and be on the same page, be sharper, be quicker, all those little things,” Singletary said. “It is not like they are covering the wrong guy. It is not like they are calling the wrong thing. I would just like for it to happen faster, that’s all. We just have to play faster.”