"This base defense consists of four defensive linemen, three linebackers, and four defensive backs (two safeties, two corners). Against two-receiver offensive sets, this formation is effective against the run and the pass. In the original 4–3, defensive tackles would line up opposite the offensive guards, and defensive ends on the outside shoulders of the offensive tackles. On passing downs, the Mike (middle linebacker) is often responsible to cover any running backs, the Sam (strong-side linebacker) covers the Tight End, and the Will (weak-side linebacker) either covers a back or blitzes in an attempt to sack the quarterback. Though first used as a base defense by the New York Giants in 1956, plenty of teams experimented with it during the 1950s, and thus there are multiple claimed inventors of this defense. There are several different variations of the 4–3 defense such as the 4-3 under defense, 4-3 over defense, 4-3 umbrella defense, 4-3 swim defense, and 4-3 slide defense." [List of formations in American football. Wikipedia]
This example diagram was redesigned from the Wikimedia Commons file: 4-3 green.svg.
This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. [creativecommons.org/licenses/by-sa/3.0/deed.en]
The American football positions diagram example "Defensive Formation - 4-3 defense" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Football solution from the Sport area of ConceptDraw Solution Park.