Defensive Play Diagram – Under Front

"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. ...
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 strongside linebacker over the tackle, and shifted the weakside tackle over center. At about the same time the Cleveland Browns frequently used a weakside shift. The Dallas Cowboys coach Tom Landry developed a "flex" variation, in order to take advantage of the quickness of his Hall of Fame tackle, Bob Lilly. In Tom Landry's original 4–3 defenses (4-3 Inside and 4-3 Outside), both defensive tackle were flexed. 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. 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. More modern versions of the 4-3 include the Tampa 2 scheme and the 4-3 slide." [4–3 defense. Wikipedia]
The American football positions diagram example "Defensive play - Under front" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Football solution from the Sport area of ConceptDraw Solution Park.