The hiring of Robert Saleh, formerly of the Seahawks and the Jaguars, signalled a move to the Seahawks style 4-3 defense. Below, I will provide a breakdown of the positions within it, and what is likely to be the depth chart at each position.

LEO

A lot of writers have described this position as the right defensive end, but in reality, it is the weak-side defensive end. This means that it’s the defensive end who aligns to the weak side of the formation (i.e where there are less opposition players or potential blockers).

The primary focus of the LEO is as a pass rusher, though they also have a key role as a backside run defender. Traditionally, LEOs have been around 6”2/6”3, around 250lbs and hugely explosive. So far, the 49ers have been using Arik Armstead in this role, who is atypical physically but has some beneficial traits. He can be a disruptive rusher from any position on the line and has the length and explosiveness to make a nuisance of himself as a backside run defender.

Nevertheless, given the signing of Elvis Dumervil, Solomon Thomas being asked to learn the LEO role and some fairly neutral reviews of Armstead’s performances thus far, it may well be that he is struggling to adjust to the role. Dumervil is undoubtedly an option at the position, especially on later downs. Solomon Thomas could also play the LEO, but is likely to be the strong-side end. Aaron Lynch and Pita Taumoepenu are also currently competing for playing time at the spot.

My depth chart: Armstead, Dumervil, Thomas, Lynch, Taumoepenu

*Italicised indicates that he is likely to be a starter elsewhere

Nose tackle

This player lines up shaded over the centre. The primary responsibility of this player is to be a force in the running game, but it is clearly useful if they can bring a pass rushing presence.

Free agent acquisition Earl Mitchell looks to be the presumptive starter at the position and has earned solid reviews so far. Behind him is Quinton Dial, who I personally feel could drop off the roster if it is a choice between him and Chris Jones for a roster spot. Jones could play as a nose tackle or as a 3-tech defensive tackle. The 49ers also have rookie D.J. Jones who would be expected to get onto the roster. Dial could find himself in trouble.

My depth chart: Mitchell, C. Jones, D.J. Jones, Dial

Defensive tackle

This position has also been referred to as the 3-tech, which is the alignment the player will often take. This means that they will often line up shaded to the outside of the guard.

This player has a key role as an interior pass rusher and run defender. DeForest Buckner has been the starter at the position thus far which should continue into the season and indeed beyond that. Buckner has all the abilities required of a 3-tech tackle and if he can improve his technique he could be a stud at the position.

Behind Buckner, we are hearing that Chris Jones has been impressing. He also has penetrating qualities, though not of the level of Buckner. Armstead, Ron Blair or Thomas could also play as a 3-tech.

My depth chart: Buckner, Armstead, Thomas, C. Jones, Blair

Strong side defensive end

This has been referred to as the left defensive end but it is actually the strong-side defensive end. Depending on how the opposition align, this player could line up on the left or on the right side of the defensive line. Other names for this position are the 4-tech or 5-tech, again depending on how the player aligns related to the tackle opposite him (either just inside him or face up to him respectively).

This player has to be highly effective against the run as well as being a dangerous pass rusher. Tank Carradine has played this role so far, but is expected to fall behind Solomon Thomas once Thomas is able to train and acclimatises to the scheme, despite Carradine’s strong performances thus far. We must consider that Thomas could end up playing the LEO which would leave Carradine here. If Thomas does play the strong side end position, we can expect him to slide inside and rush from the interior on passing downs to get Carradine or another edge player onto the field.

Armstead, Buckner or Blair could also play this position and would likely be expected to kick inside in much the same way as Thomas on passing downs.

My depth chart: Thomas, Carradine, Buckner, Armstead, Blair

SAM linebacker

The strong-side linebacker is invariably on the defensive line when he is on the field, aligned to the outside of the strong side defensive end. This is essentially the same position as the 3-4 OLB, hence why Ahmad Brooks is at the top of the depth chart. In nickel and dime packages, this is normally the linebacker to leave the field.

The SAM linebacker must be able to set the edge, rush the passer and drop into coverage if necessary. Brooks has earned solid reviews for his performances so far and is backed up by Eli Harold. We hear Dekoda Watson and UDFA Jimmie Gilbert are next on the depth chart.

My depth chart: Brooks, Harold, Watson, Gilbert

MIKE linebacker

The middle linebacker is the quarterback of the defense. He has the primary communicator and has a key role in the running and passing games.

Navorro Bowman is the presumed starter at MIKE linebacker but will have competition from Reuben Foster and Malcolm Smith. Brock Coyle is another option.

My depth chart: Bowman, Foster, Smith, Coyle

WILL linebacker

The weak-side linebacker tends to draw tougher coverage responsibilities than the MIKE as well as being the most likely to be unblocked on running plays. He should theoretically be able to flow to the ball carrier unhindered owing to the MIKE drawing a block and his linemen keeping blockers off him.

Reuben Foster, when fit, is expected to be the WILL linebacker but Malcolm Smith has earned high praise so far this offseason. We could see the two of them and Navorro Bowman rotating frequently across the two linebacker spots. Ray-Ray Armstrong is another option at the WILL linebacker spot.

My depth chart: Foster, Smith, Armstrong, Bowman

Outside corner

This scheme calls for long, press-cover capable corners.

The 49ers have one starter seemingly nailed on in Rashard Robinson but across from him an open competition between Keith Reaser, Dontae Johnson and Ahkello Witherspoon is brewing. Reaser appears to have the advantage right now, but arguably is only ahead of Witherspoon because of Witherspoon’s lack of experience. By the regular season, Witherspoon could be across from Robinson. Prince Charles Iworah and Will Redmond could also play outside.

My depth chart: Robinson, Witherspoon, Reaser, Johnson, Redmond, Iworah

Nickel corner

The nickel corner is responsible for covering slot receivers as well as intermediate zones when the 49ers are in the nickel or dime defense.

Free agent acquisition K’waun Williams is the current favourite to start at nickel, backed up by Will Redmond. If Reaser fails to win the starting job at outside corner, he could compete for a chance to play at nickel.

My depth chart: Williams, Redmond, Reaser

Strong safety

The strong safety is essentially a pseudo-linebacker in this scheme. He allows the team to have an 8 man box and has significant responsibilities in the running and passing game.

Eric Reid is the starter at the position at this point but Jaquiski Tartt will likely run him close and has the talent to see the field early and often. Given the past coverage struggles of Bowman and Smith (plus the difficulty in transitioning from college pass coverage to NFL pass coverage for Foster), we could see the 49ers heavily utilising three safety looks on passing downs to get Tartt and Reid on the field together. UDFA Chancellor James is the third name on the depth chart.

My depth chart: Reid, Tartt, James

Free safety

The free safety, is the “eraser” of this defense. Frequently playing as a single high safety, the free safety has enormous responsibilities in the passing game but must also be capable of mixing it up against the run.

Jimmie Ward is the starter at the position and though we haven’t heard much about him so far, the reported focus of the offense on short passing goes a long way toward explaining this. Unless an offense is launching bombs, 49ers fans should want to hear as little about Ward as possible.

Behind Ward are Vinnie Sunseri and highly touted rookie UDFA Lorenzo Jerome. Jerome should overtake Sunseri soon, but it is likely that Tartt will be the first choice backup for either safety should they go down hurt.

My depth chart: Ward, Tartt, Jerome, Sunseri