San Francisco 49ers: Breaking down how the 4-3 defensive line will work

The San Francisco 49ers have switched to a 4-3 base alignment, and Niner Noise breaks down how the defensive line will both look and work this upcoming season.

Now that free agency and the NFL Draft are in the rear-view mirror, we have a better grasp of who is going to be on the San Francisco 49ers’ 53-man roster and, more specifically, who is going to play a major role in each respective positional group.

Transitioning from a 3-4 base alignment to a 4-3 means that some outside linebackers in the old defense are going to be playing with a hand on the grass while playing defensive end.

Additionally some players, who played on the outside of the line, might have to kick inside to play the 3-technique.

San Francisco 49ers

All in all, there is going to be new personnel managing a different defensive technique in San Francisco this season.

To understand where the players are going to fit, it is crucial to understand the 4-3 defensive front the 49ers plan to employ under coordinator Robert Saleh.

This defensive ideology comes from the Pete Carroll coaching tree, which has had significant success at the NFL level, as coaches Dan Quinn and Gus Bradley have most recently deployed it with rave reviews. The key for the defensive line in this scheme is versatility.

The need for depth and versatility is paramount, as the D-line must have several different rotations in order to succeed. The base defense has the LEO, a 3-technique, a 1-technique and a 5-technique.

The LEO is the primary edge rusher and was the biggest question mark for the 49ers prior to training camp. The 3-tech is the smaller of the tackle positions and therefore expects to be quicker than the 1-technique. This player lines up across to the guards outside shoulder. The 1-tech lines up between the guard and the center and are almost always the biggest player on the defense. This player will take on double teams, be critical in the run game, and must create gaps for pass rushers.

Let’s start with the three players most 49ers fans are most concerned with: Arik Armstead, DeForest Buckner and Solomon Thomas.

All three are versatile, with none of the three having a clear position in any defensive scheme. Some view this as a negative, while other defensive coordinators lick their chops with the potential to confuse quarterbacks by mixing up the defensive looks and line schemes. Although each player is versatile, they are all distinct from one another and can play together on the same defensive line.

The oldest of the three, Armstead is 6-foot-7 and just shy of 300 pounds. The third-year pro has battled injuries in his brief career but is hoping to have put his injury woes behind him, following labrum surgery this offseason. Armstead has shown flashes of greatness in his first two years in San Francisco, logging an impressive 11.8 pass-rush productivity mark, per Pro Football Focus (h/t @49ersHive):

The defense in 2017 might not dazzle, statistically, but this team will show flashes of greatness.

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This positional group is loaded with first-round talent, as the 49ers have spent their last three top draft picks fortifying this area. Armstead, Buckner, Thomas and Earl Mitchell look to be the key cogs in the D-line, with Ahmad Brooks, Ronald Blair, Aaron Lynch, Tank Carradine and rookie D.J. Jones filling in as rotational players.

Without knowing exactly who will be playing where, it’s clear this line will intimidate quarterbacks.

Let’s go back to the LEO position. This player will be going one-on-one on the weak side and must have the capability to get to the quarterback. Hence the question mark, as the team only had 33 total sacks last season. I think this position will see a variety of players work here this season, including the pass-rushing veteran, Elvis Dumervil. And with none likely to dominate in this role, I foresee this being a season-long rotational position.

I project Dumervil, Lynch, Armstead and Solomon Thomas to all get long looks at the LEO.

Next: 49ers film room: Roster fits in Robert Saleh's defense

Ideally, Armstead will fill this role full time, and become a menace for left tackles.