49ers: Defensive Position-by-Position Breakdown and Depth-Chart Analysis

With training camp less than a month away, it’s time to break down what the San Francisco 49ers’ depth chart might look like in 2015. Let’s start with the defense.

On the base defensive line, the Niners may trot out three nose tackles (Ian Williams, Glenn Dorsey and Quinton Dial) and play two of them at defensive end. They would give the Niners a stout run defense.

In the sub-packages, the Niners may take all three nose tackles off the field and replace them with interior pass-rushers. We might see frequent substitutions next season on the defensive line.

We might see a rotation of linebackers, as well. The same goes for the secondary. This is all new stuff for the 49ers, who rarely rotated players under the previous defensive coordinator, Vic Fangio.

With that in mind, here is a position-by-position breakdown of the Niners defense.

Defensive Line

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Arik Armstead (above) is the 49ers' heir apparent at defensive end.

Left defensive end: Quinton Dial, Darnell Dockett, Arik Armstead

Nose tackle: Ian Williams, Glenn Dorsey, Quinton Dial

Right defensive end: Glenn Dorsey, Tank Carradine

Rising: Arik Armstead

First-round pick Arik Armstead probably will start training camp at the bottom of the depth chart, because he missed OTAs and minicamp and he’s only 21.

But Armstead probably is the most talented player on the 49ers’ defensive line. If he plays well during training camp and preseason, he may earn a role in the 49ers’ base defense or sub-packages—especially if veteran defensive lineman Darnell Dockett continues to miss time due to a torn ACL he suffered last August.

Falling: Darnell Dockett

Former Arizona Cardinals defensive lineman Darnell Dockett probably won’t play in the 49ers’ base defense next season because he’s a poor run-blocker.

The Niners probably will use Dockett primarily as an interior pass-rusher in the sub-packages, although someone might take that role from him if he misses the entire offseason rehabbing his torn ACL.

Standing on shaky ground: Quinton Dial

Third-year vet Quinton Dial is in line to replace Ray McDonald at left defensive tackle in the base defense next season.

Dial seems in terrific shape, but it’s only a matter of time before Armstead takes his job. That's what the Niners drafted Amstead to do. He is the heir apparent, and Dial is merely the placeholder.

Dial's future will be at nose tackle if Ian Williams leaves via free agency in 2016.

Outside Linebacker

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Left outside linebacker: Ahmad Brooks, Aaron Lynch

Right outside linebacker: Aldon Smith, Corey Lemonier, Eli Harold

Rising: Eli Harold

As a courtesy of the four veteran outside linebackers, rookie third-round draft pick Eli Harold probably will start training camp at the bottom of the depth chart.

But that courtesy won’t last long. If Harold outperforms the veterans in August, as he did in May and June, the Niners coaches will have no choice but to bump him up the depth chart.

Falling: Corey Lemonier

Former 2013 third-round pick Corey Lemonier has been a disappointment. In two years, he has just one sack. He seems to have no pass-rush moves.

The Niners probably will give him the rest of the offseason to prove himself and turn his career around. But if he continues to struggle, the Niners might decide to cut him. Four outside linebackers might be more than enough for San Francisco.

Standing on shaky ground: Ahmad Brooks

Thirty-one-year-old starter Ahmad Brooks is standing in the way of two talented young outside linebackers: Harold and Aaron Lynch.

If either of them outplays Brooks in the preseason—which is possible; Lynch outplayed Brooks during the 2014 regular season—the Niners could look to trade Brooks to a team that needs a starting outside linebacker.

Inside Linebacker

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Left inside linebacker: Michael Wilhoite, Nick Bellore

Right inside linebacker: NaVorro Bowman, Nick Moody

Rising: Nick Moody

Nick Moody was a special teams specialist at Florida State. The 49ers have been trying to turn him into an inside linebacker since they drafted him in the sixth round two years ago.

Moody needed to develop inside-linebacker instincts, which takes time. But according to 49ers’ head coach Jim Tomsula, Moody seems to be improving. “A guy that’s really moving and feeling the defense the right way is Nick Moody,” Tomsula said, according to Matt Barrows of the Sacramento Bee.

If Moody continues to improve, he might compel defensive coordinator Eric Mangini to use a three-man rotation at inside linebacker.

Falling: Michael Wilhoite

Fifth-year vet Michael Wilhoite is a decent coverage linebacker, earning a plus-2.1 coverage grade in 2014 from Pro Football Focus. But Wilhoite is not-so-good against the run. Pro Football Focus gave him a minus-7.0 run-defense grade last season.

If the 49ers can find a better run-defending inside linebacker (like Moody), they might relegate Wilhoite to sub-packages and special teams.

Standing on shaky ground: Nick Bellore

Twenty-six-year-old Nick Bellore isn’t really an inside linebacker—he’s a special-teams coverage specialist. The Niners may decide they need extra depth behind NaVorro Bowman at inside linebacker, and Bellore might not be good enough to provide it.

In that case, the 49ers could choose to keep veteran Philip Wheeler instead of Bellore.

Safety

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Strong safety: Antoine Bethea, Craig Dahl

Free safety: Eric Reid, Jaquiski Tartt

Rising: Jaquiski Tartt

Rookie second-round pick Jaquiski Tartt currently is competing for a role in the 49ers dime package (six defensive backs). But if starting free safety Eric Reid has another down season or suffers a fourth concussion, Tartt might replace him. Tartt is breathing down Reid’s neck.

Falling: Craig Dahl

Eight-year vet Craig Dahl made a career for himself on special teams. As a safety, he’s lousy and has proven that time and time again. If a young safety such as L.J. McCray or Jermaine Whitehead outperforms Dahl on special teams during the preseason, the Niners will probably cut Dahl.

Standing on shaky ground: Eric Reid

Former 2013 first-round pick Eric Reid went to the Pro Bowl his rookie season. He seemed like the second coming of Ronnie Lott. 

But not during season No. 2. Reid was up-and-down in 2014, and he has suffered his third concussion. As a result, the Niners spent their second-round pick on a free safety, Jaquiski Tartt.

Reid has to fight for his future on the 49ers, or else Tartt will take it from him.

Cornerback

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Keith Reaser (above) seems to be climbing the 49ers' depth chart.

Left cornerback: Tramaine Brock, Dontae Johnson

Slot cornerback: Jimmie Ward, Dontae Johnson, Keith Reaser

Right cornerback: Shareece Wright, Chris Cook, Keith Reaser

Rising: Keith Reaser

Former 2014 fifth-round pick Keith Reaser gave up only a couple of catches in front of the media during OTAs and minicamp this offseason. He played like a shutdown corner.

He missed his rookie season due to a torn ACL, but he’s healthy now. And he might be the Niners’ best cornerback. He’s big (6’0”, 190 lbs), fast (4.3-second 40-yard dash) and has loose hips which allow him to mirror receivers in man coverage.

He’s the total package.

Falling: Dontae Johnson

One round before the Niners drafted Reaser, they drafted former North Carolina State defensive back Dontae Johnson.

Johnson mostly played safety in college, although he played some cornerback. The Niners played him at cornerback last season, and he struggled, especially outside. But he was decent in the slot.

Johnson continued to struggle when he lined up outside during OTAs and minicamp this offseason. He gives up too much separation near the sideline. His best role might be slot cornerback in the red zone, because he’s tall (6’2”).

Standing on shaky ground: Shareece Wright/Jimmie Ward

Before the offseason began, Shareece Wright seemed like the favorite to start at right cornerback, and Jimmie Ward seemed like the favorite to start in the slot for the 49ers.

But both players suffered injuries and missed all of OTAs and minicamp, while Reaser played out of his mind. If Reaser keeps playing that well, he will probably take the place of Wright or Ward in the Niners’ starting lineup.

All quotations and practice observations obtained firsthand unless otherwise noted.

Follow @grantcohn.