The 3-4 defense has caught on in recent years among NFL teams, but why? What is so different, or better, about this scheme that has teams seemingly running to it. Let's start out by defining what a 3-4 defense is.
The term 3-4 refers to the number of linemen and linebackers, respectively. So there are 3 down linemen and 4 linebackers.
This is desirable for many teams because it allows for two immediate advantages. First, it allows you to get better athletes on the field. Linebackers are typically more athletic than linemen. They can run faster, they are more agile, and they are more versatile. Second, because you have more athletic versatile athletes on the field it allows the coach to use his players differently. This second point is the main selling point of the 3-4.
In the NFL games our won and lost on split second decisions. Being able to confuse the opposing quarterback for even the slightest amount of time can make a world of difference. By having these versatile linebackers on the field the coach can better disguise his defensive scheme. He can have any combination of those 4 linebackers blitz or drop into pass coverage. This also helps on the exotic safety and corner blitzes because the linebackers can pick up pass coverage in the short zone. All of these options come from the versatility of having 4 linebackers instead of only 3.
Because the scheme is different than the traditional 4-3 it requires a slightly different type of player. Even though the 3-4 is a scheme designed for the linebackers to make plays the nose tackle is the most important part of the defense. This is because there are only 3 linemen so each one has added responsibility. The nose tackle is the one who has to plug up the middle of the line; he also has to be big enough, and talented enough to be able to occupy at least 2 offensive linemen on rushing plays. If he can't do this the offensive linemen will be able to get to the linebackers and block them. Since the linebackers are your play makers you can't afford to have them being blocked. The nose tackle has to control the entire middle of the line. This usually requires a much bigger man than you find on the defensive lines of teams using the 4-3 scheme. Also most colleges run a 4-3 so finding a true 3-4 nose tackle is rare.
In the 3-4 there are 3 linemen over the offensive line and the 4 linebackers about 5 yards behind them. Now imagine what would happen if the offense could consistently dominate the middle of the line by pushing around the nose tackle. They would be able to gash the defense for huge rushing yards all game. Because of this he is the most important player on any team running a 3-4.
The linebackers are not all that different from those in a 4-3. The two middle linebackers are the same as a middle linebacker in a 4-3. They need to be strong against the run and be able to shed blockers and make tackles in the middle of the field. The two outside linebackers have basically the same responsibility as the two outside linebackers in a 4-3. They need to have enough speed to be able to effectively rush the quarterback or drop into pass coverage. They also have to be able to cover a back coming out of the backfield into a passing route, and make the tackle in the open field. The outside linebacker position emphasizes athleticism and speed over size and strength as compared to the inside linebacker.
The 3-4 requires a slightly different type of player and because of that the switch to it can't be made overnight. Trades and drafting have to be done ahead of time to effectively plan for the change. However, once the right personnel is in place the 3-4 defense can pay huge dividends with the versatility it offers a team.
