The nose tackle is also known as the nose guard. The nose tackle line up directly over the offense’s center. A nose tackle is employed more often in 3-4 defensive schemes than in 4-3 defensive schemes, which tend to line their two defensive tackles in the gaps between the center and guards, or directly over the guards.
In the 3-4 defense, the nose tackle is meant to take on the center and force a double-team, hopefully freeing up a linebacker to make the tackle. In this way, the nose tackle becomes a kind of blocker for the defense’s linebackers.
Because of this, the nose tackle is usually the largest player on the defense, and often the largest player on the field. The nose tackle is supposed to be strong enough and durable enough to routinely take on two blockers without being pushed off the line of scrimmage. Therefore, strength, size and leverage (many are shorter than the average defensive end) are a premium with the nose guard.
What a Nose Guard Does
A nose guard or nose tackle generally will not have many measurable statistics. That’s because his purpose is not to get to the quarterback or the running back, but to force a double-team. This double team theoretically frees other defensive players to make plays. Therefore, one cannot know the effectiveness of a nose tackle by looking at his stats.
Instead, it is better to see if the nose tackle is holding his position along the "point of attack" or line of scrimmage, as well as attracting two blockers on most plays. If he is doing both of these, then any statistical production by the nose tackle is a bonus. If a nose tackle is consistently being pushed downfield by his blockers, or if the center is able to block the nose tackle by himself, then the nose tackle is not doing his job.