Seven-man line defense

The seven-man line defenses are defensive alignments in American football that utilize seven "down linemen", or players on the line of scrimmage at the time of the snap. While now obsolete as base defenses, these were the most prominent alignments before the forward pass became prevalent and remained in use for some time thereafter. The two most common variants were the 7–2–2, or seven-box defense, and the 7–1–2–1, or seven-diamond defense.

Overview
The 1906 football rule reforms mandated that offenses use at least seven down linemen. These players usually stood shoulder-to-shoulder before the snap, a posture defenses tended to match. The defenses of the time are considered unsophisticated by today's standards. The interior defensive linemen were expected to hold their ground against their assigned blockers, while the responsibility of disrupting the offense rested primarily with the tackles and ends, especially those lined up on the "strong" side of the opposing line.

Improvements in offensive blocking schemes eventually made the seven-man line defenses vulnerable, but it remained a common formation, particularly against opponents with an unreliable passing attack, even into the 1950s.

The 3-4 defense can be seen as a modern variant of the 7-man defensive front (specifically the 7-2-2), with the cornerbacks (ends), outside linebackers (tackles), "defensive ends" (guards) and the nose tackle (center) all lined up roughly on the line of scrimmage. The key difference is in the spacing of the line (the linebackers and defensive ends are spread much wider than in a traditional 7-man front) and the fact that the outside linebackers and cornerbacks usually stand upright instead of crouching into a three-point stance.

7–2–2 defense
The 7–2–2, or seven-box defense, used two linebackers, and two safeties. Amos Alonzo Stagg invented the seven-box defense in 1890 at Springfield College. At that time, most teams were using a nine-man line on defense, and there were only three downs and no forward passes. The 7–2–2 was the base defense used by Knute Rockne at Notre Dame. Into the late 1930s, the 7–2–2 was still commonly employed inside the defender's thirty-yard line. It was considered "very strong against a running attack, but rather weak defensively against passes." The 7–2–2 was also employed when the opponent was expected to punt.

7–1–2–1 defense
The 7–1–2–1, or seven-diamond defense, used one linebacker, two safeties relatively close to the line and one safety farther downfield. The formation was created by Minnesota coach Henry L. Williams in 1903, reputedly to stop Michigan back Willie Heston. By the mid-1930s, the 7–1–2–1 was considered "almost obsolete" due to its weakness against the forward pass, whereas the 7–2–2 was still considered viable.