The San Francisco 49ers are soon expected to announce Jacksonville Jaguars Linebackers Coach Robert Saleh as their new Defensive Coordinator. Saleh has been with the Jaguars for the past three years helping run their 4-3 defense, and it appears that is also what he’ll be running in San Francisco, according to ESPN’s Adam Caplan.
For those asking: 49ers expected to run 4-3. Same as Gus Bradley's defense. Some coaches say has elements of a 3-4 on tape.
— Adam Caplan (@caplannfl) February 14, 2017
This will be a departure from the 3-4 style the 49ers have run for a number of years, but not a complete restructure. Saleh is expected to implement the 4-3 under defense that former Seahawks Defensive Coordinator and Jaguars Head Coach Gus Bradley uses, which is actually very similar to a 3-4 defense. Though the 49ers roster will be different next year, most of the starters are probably already in place, and we can reasonably guess which roles they’ll play.
There are three linebackers in a 4-3: The WILL, who lines up over the left side of the offense, the MIKE, who is near the middle, and the SAM, who lines up over the right side. What makes the 4-3 under defense different from a normal 4-3 is that the SAM will often line up on the line of scrimmage, like a 3-4 outside linebacker. The WILL right now would be Ray-Ray Armstrong, the team’s most athletic linebacker. The MIKE, the “captain” of the defense, would likely be NaVorro Bowman. The SAM position would go to Ahmad Brooks.
One key difference between the 4-3 under and 3-4 is that in the latter, the best pass rushers are the outside linebackers. In the former, that distinction goes to the defensive lineman. The LEO, often the team’s best pass rusher, lines up across from the left tackle. Though he is technically a defensive lineman, the LEO is more like a 3-4 outside linebacker in that he needs to be athletic enough to beat tackles around the edge. Currently the 49ers best pass rusher is Aaron Lynch, so the LEO role would be his.
Next to the LEO is the 3-Tech, who lines up between the left tackle and left guard. This player is usually the team’s best pass rushing interior lineman and arguably the most important position on this defense. This player must be able to win one-on-one consistently, because the 4-3 under defense is designed to give this player one-on-one looks. This is the primary position superstar defensive tackle Aaron Donald plays for the Los Angeles Rams. This one is a toss-up between Arik Armstead and DeForest Buckner. Ideally, the 3-Tech would be shorter than these two, but they are the team’s best interior rushers.
The 1-Tech is essentially the same as the nose tackle in a 3-4. Their job is to line up across from the Center and clog up the middle. He will usually be the biggest, most powerful player on the defense, but typically shorter (Think former Seahawk Brandon Mebane). He is responsible for defending runs that go inside either guard. The 49ers don’t currently have someone suited for this role. Nose tackle Ian Williams was released earlier this year and has recurring injury issues. The 49ers need to upgrade here this offseason.
Finally, there’s the 5-Tech (also called the 4-Tech), who lines up across from the right tackle. His job is essentially the same as the 1-Tech: Stop the run. This player is a 3-4 defensive end with a different name. This would be whichever of Armstead or Buckner loses the battle to be the 3-Tech.
This is a very simplified version of what a 4-3 under defense looks like, but we can probably expect to see the 49ers field something similar next year.
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