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49ers 2017 Season: San Francisco’s new run defense

By Jonah Burros

Dec 20, 2015; Santa Clara, CA, USA; San Francisco 49ers inside linebacker NaVorro Bowman (53) celebrates after the 49ers recovered an onside kick during the fourth quarter at Levi's Stadium. The Cincinnati Bengals defeated the San Francisco 49ers 24-14. Mandatory Credit: Ed Szczepanski-USA TODAY Sports
Dec 20, 2015; Santa Clara, CA, USA; San Francisco 49ers inside linebacker NaVorro Bowman (53) celebrates after the 49ers recovered an onside kick during the fourth quarter at Levi's Stadium. The Cincinnati Bengals defeated the San Francisco 49ers 24-14. Mandatory Credit: Ed Szczepanski-USA TODAY Sports /
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Sep 27, 2015; Glendale, AZ, USA; Yardage chains sit on the field prior to the game between the Arizona Cardinals and the San Francisco 49ers at University of Phoenix Stadium. Mandatory Credit: Joe Camporeale-USA TODAY Sports
Sep 27, 2015; Glendale, AZ, USA; Yardage chains sit on the field prior to the game between the Arizona Cardinals and the San Francisco 49ers at University of Phoenix Stadium. Mandatory Credit: Joe Camporeale-USA TODAY Sports /

The scheme

The base 4-3 under scheme and its history were talked about extensively in part three of this series when we analyzed the pass defense. You can review this article here.

To recap exactly what this defense is designed to do, I will stress the fact that it basically puts the team in an advantage facing the run and rushing the passer.

It accomplishes this by giving the defensive lineman and inside linebackers assigned gap control instead of reading a blocker and choosing a side that the run might go to. Here is a graphic that shows the basic front alignment in regards to a base pro-style offense:

Everything is predicated off of the strong side of the formation, that would be wherever the tight end lines up.

The defensive tackles are key to eating up blocks through an assigned gap, here, the strong side DT is the nose guard and plugs the A-gap on the strong side while the weak side DT plugs the B-gap on the weak side.

The spacing on either side of them is the responsibility of the inside linebackers. The MIKE ILB shoots the B-gap on the strong side while the WILL ILB does the same for the A-gap on the weak side.

What makes this defense different from most is the assignments of the defensive ends and SAM LB.

The strong side DE is primarily a run stopper that controls the strong side C-gap while the weak side DE tends to be a dedicated pass-rusher that burns around or through the weak side C-gap responsibility in order to get to the quarterback.

The SAM LB controls everything on the inside of the TE on the strong side of the play. This means that he looks for sweeps, screens, off-tackle runs but also covers the TE on routes and in the flats. He is backed up by his strong side safety and corner or a scraping ILB following the play.

There are extra responsibilities for the SAM ILB and secondary players but the inside five have the freedom to bull-rush their assigned gaps with a quick jump off of the snap and blow up the play. It is difficult to run inside against a gap shooting front and the outside is where things tend to get tricky.

As we talked about in part three, the SAM and weak side DE or “Elephant” positions are very important to the pass defense and pass rush. For the purpose of addressing the base run defense, we should examine the ILBs and the defensive line across the board.

This is where the 49ers base front lives and breaths in stopping the run and could give us a glimpse into the starting lineup.