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In American football, a 4–3 defense is a defensive alignment consisting of four down linemen and three linebackers. It is probably the most commonly used defense in modern American football and especially in the National Football League. ==History== Early in the history of the NFL, teams stacked the defensive line of scrimmage with seven linemen, typically using a 7-diamond or the 7-2.〔Owen, Steve, p. 177〕 With the liberalization of the forward passing rules in 1933, the defenses began to evolve along with the offensive changes, and by the later 1930s, the standard defense in the NFL and college was the 6-2.〔Halas, pp. 167–170〕〔Owen, Steve, pp. 178–179〕 The successes of the T formation in the 1940s led to the almost universal adoption by 1950 of the five-man line.〔''Total Football II'', chapter 17.〕 There were two versions popular in the NFL. The 5-3 was an older defense that remained popular through the 1940s and early 1950s. But by the late 1940s, Greasy Neale's defense was creating problems for offenses with a five-man line and four-man secondary. Roughly concurrently, Paul Brown had developed a vertical timing offense. The Browns won every championship of the rival All-America Football Conference from its inception in 1946 through 1949. In the first game of the 1950 season NFL Commissioner Bert Bell had the newly admitted Browns play the champion Philadelphia Eagles on a Saturday ahead of the rest of the league's scheduled Sunday games. The Browns handily won the game in Philadelphia 35–10 and showed they were a force to be reckoned with. Defenses knew they had to find a way to stop the spread-out vertical offense of the Browns and the New York Giants head coach Steve Owen came up with his umbrella defense which showed a 6–1–4 alignment before the snap but could flex (drop back) its two defensive ends into pass protection. The defense was successful, and the only two losses by the Browns in 1950 came at the hands of the Giants. While the concept belonged to Owen, the newly acquired defensive back, Tom Landry, explained and taught the defense.〔''Tom Landry: an Autobiography'' ISBN 0-310--52910-7〕 While the defense was a precursor to the traditional 4–3–4 of today, it was not yet evolved into what one would call a traditional 4–3 defense. That took an additional six years. Other NFL teams came to a version of the 4-3 via a different route. Despite the success of the Brown in the single game with the Eagles, the 5-2 Eagle became more popular, and more teams began to switch to it from the older 5-3 defense.〔 Because the 5-2 lacks a middle linebacker, it was vulnerable to passes over the middle. As a consequence, 5-2 teams experimented with pulling their middle guards back, and many teams were trying this new approach by 1954.〔Zimmerman, p. 128〕 In 1956, Landry became the first defensive coordinator to switch to the 4-3 as a base defense. As the 1956 Giants won the NFL Championship, this gave the 4-3 enormous exposure, and just about the whole NFL converted to the new system the following season.〔 In the original version of the 4–3, the tackles lined up over the offensive guards and the ends lined up on the outside shoulder of the offensive tackles, with the middle linebacker over the center and the other linebackers outside the ends. In the mid-1960s, Hank Stram developed a popular variation, the "Kansas City Stack", which shifted the strong-side defensive end over the tight end, stacked the strong-side linebacker over the tackle, and shifted the weak-side tackle over center. At about the same time, the Cleveland Browns frequently used a weak-side shift. Landry developed a "flex" variation, in order to take advantage of the quickness of his Hall of Fame tackle, Bob Lilly.〔Golenbock, p. 233〕 In Landry's original 4–3 defenses (4–3 inside and 4–3 outside), both defensive tackles were flexed.〔Lombardi, pp. 173–185〕 In the "flex", on a pro set right, with defensive keys showing a run to the right, the right defensive tackle would be flush on the line and was supposed to penetrate.〔Golenbock, pp. 232-240.〕 The right defensive end and left defensive tackle were flexed two feet off the line of scrimmage, the right defensive end now head-on with the left offensive tackle (i.e. a 4–2–2–5 front instead of the more common 5–2–2–5 front). This gave the defense a "zig zag" look unlike any other of its day. The 'flex' was developed to counter option blocking by the offensive lines which had learned to move their heads up defensive linemen to either side to create holes. The running back would then patiently run to daylight. The Flex allowed two defensive linemen to read and react better to the option blocking. The other two linemen could either attack upfield or hold their single gap like the flexed linemen and wait for the ball to come to them. These concepts of shooting the gap and shoot and holding the gap are integral parts of today's more modern versions of the 4–3 which include the Tampa 2 scheme, the Seattle Seahawks shoot and hold defense and the 4–3 slide. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「4–3 defense」の詳細全文を読む スポンサード リンク
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