Why is the 49ers defense so good over the middle of the field?

The 49ers pass defense has really struggled this year. They are 20th in the league giving up 231 yards per game. That is due in large part to their outside corners not being very good. Ahkello Witherspoon is PFF’s 54th ranked corner and Dontae Johnson is PFF’s 166th ranked corner. There will be opportunities for Rishard Matthews and Corey Davis in this one.

San Francisco’s DVOA numbers tell a similar story. They are 29th against the pass, 27th against #1 receivers, 25th against #2 receivers but 4th against tight ends. When you look at it by direction, they are 31st against passes to the left side of the field, 30th against passes to the right side of the field but 4th against the tight end.

I asked David Fucillo of Niners Nation what makes them so good in the middle of the field:

The reason for success against tight ends and over the middle is two people: Eric Reid and Reuben Foster. The 49ers run a Seahawks style of defense with a single deep safety, and then a strong safety down inside the box. Eric Reid had played free safety, but this year he is playing that Kam Chancellor in-the-box role. Reid is not the greatest when it comes to the previous deep role, but he was capable in it. That gives him a strength in covering players in the middle of the field, and he has excelled there.

Foster was one of the 49ers two first round draft picks this past year. He is playing the weak side linebacker role, but he'll take over the middle linebacker next year. Foster slipped to the end of the first round due to questions about his shoulder and general durability. He missed over a month with a high ankle sprain, and injuries remain a concern. But, he won defensive rookie of the month for November, leading rookies in tackles in spite of the 49ers having their bye that month. But he brings tremendous athleticism, and that's part of how he can cover tight ends. He is great defending the run, but has the speed and athleticism to drop into coverage.

The reason the 49ers struggle outside is inconsistency from their cornerbacks. Rookie Ahkello Witherspoon is showing improvement each week, but a rookie corner is still a rookie corner. It's a developing process for him. Fourth year veteran Dontae Johnson starts opposite him, and has had his own share of inconsistency. He was destroyed by DeAndre Hopkins last week, and particularly good wide receivers will likely continue to give the 49ers trouble this season.

Aside: I love me some Reuben Foster!

We know that Delanie Walker is a huge part of the Titans passing game. Terry Robiskie should be scheming some things up to get Walker opportunities, but he is probably just watching tape of the long Derrick Henry 4th quarter runs over and over.