On Wednesday, ESPN.com’s Mike Sando wrote a blog theorizing the 49ers could switch from a 3-4 defense to a 4-3 defense at some point in the distant future. With all due respect to Sando, the 49ers’ defense already is a 4-3 defense. They just use 3-4 personnel.
First of all, the 49ers use a classic four-man defensive line more than 65 percent of the time, in their sub packages. On base downs, the 49ers use a nose tackle, but that does not mean they use a 3-4. In a 3-4, the nose tackle lines up directly over the center in a zero-technique position, and the ends line up on the outside shoulder of the offensive tackles in a five-technique position – creating three “bubbles” at the line of scrimmage. The 49ers don’t do this.
The 49ers base defense is a 4-3 Under, a variation of a four-man line. The defensive ends are not five-techniques. The ends are reduced, or “eagled down,” over the outside eye of the guards to three-techniques, and the outside linebacker – Aldon Smith – essentially is a stand-up defensive end.
The nose tackle is a one gap player. He lines up between the center and guard in one-technique position. The strong safety usually plays the eighth-man-in-the-box concept, even from depth, just so nobody along the front has to be a two-gap defender.
Glenn Dorsey, the 49ers’ newest defensive tackle, played five-technique for the Chiefs and was not successful, but the 49ers will not ask him to play five-technique. They’re going to ask him to play three-technique or one-technique, classic 4-3 positions, the positions he played in college.