Offense is action, defense is reaction. At least that's how things used to be, until the 46 defense and now the zone blitz started dictating terms.
In football's early days the popular defense was the 7-diamond, made up of seven linemen, a fullback (who later became known as a linebacker) behind them, two halfbacks on the flanks and a safety in the deep middle. The 7-diamond was a mirror of the offensive formation, and it was designed to stop the power game that was prevalent in football's Stone Age.
The forward pass mothballed the 7-diamond, and in the 1930s the standard defense became the 6-2, with a more mobile linebacker replacing one of the linemen. When Clark Shaughnessy, a consultant to the Chicago Bears, developed the T formation with a man in motion in the 1930s, the defense loosened further, to a 5-3, and then, in the 1940s, to Philadelphia coach Greasy Neale's Eagle-5, a 5-2 alignment with two cornerbacks and two safeties.
But in a historic Saturday-night game, on Sept. 16, 1950, in Philadelphia, Paul Brown's All-America Conference champion Cleveland Browns crushed Neale's NFL champion Eagles 35-10 with sideline passes to the Browns' spread ends, Dante Lavelli and Mac Speedie, and traps and draws up the middle by 238-pound Marion Motley. Sitting in the stands that night was New York Giants coach Steve Owen, whose team was scheduled to play Cleveland the following week.
To counter Brown's attack, Owen installed a 6-1-4 defense, with his ends, Jim Duncan and Ray Poole, "flexing," or dropping back as linebackers. It was the forerunner of the modern 4-3, and it was nicknamed the Umbrella Defense. Owen's left cornerback and brightest defensive player, 25-year-old Tom Landry, had the assignment of putting the scheme on the blackboard. The result was a 6-0 New York win, the first time that Brown had been shut out.
The 4-3 was the standard NFL defense until 1974, when New England Patriots coach Chuck Fairbanks and Houston Oilers defensive coordinator Bum Phillips decided that the collegiate 3-4 was the way to travel in the NFL. (Fairbanks and Phillips had previously coached at Oklahoma and Oklahoma State, respectively.) The 3-4 had been used before. In the '60s the Oakland Raiders occasionally dropped left tackle Dan Birdwell into a linebacker position, and in 1971 and '72 the Miami Dolphins brought in a fourth linebacker, Bob Matheson, for passing situations, but no one had ever used the 3-4 as a base defense. At first it was thought to be soft against the run, but by the early 1980s it was the defense of choice for all but eight of the NFL's 28 teams.
The desire for a stronger pass rush brought back the 4-3 and prompted Chicago defensive coordinator Buddy Ryan to devise a terrifying monster called the 46, named after his wild-man strong safety, Doug Plank, who wore that number. The 46 was the ultimate in pressure: eight men stacked near the line, every gap covered, incessant blitzing. It catapulted the Bears to the Super Bowl title in January 1986, but as it came into vogue around the league, defensive coordinators sadly discovered that without Ryan's collection of talent, led by middle linebacker Mike Singletary, it was highly vulnerable. Teams could get outside it. The 46 gave up too many big plays, as cornerbacks wore down from constant man-to-man coverage.
Enter the zone blitz. Again pressure is the main feature, only this time it comes from an intricate blitz package featuring linebackers and defensive backs firing in from all angles, with defenders—sometimes linemen—dropping into zones behind them. Zone defenses have been in football since the 1930s, but the idea of using a zone to back up a blitz package is unorthodox.