Defensive formation - 4-3 defense

"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.
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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.

"The I formation is one of the most common offensive formations in American football. The I formation draws its name from the vertical (as viewed from the opposing endzone) alignment of quarterback, fullback, and running back, particularly when contrasted with the same players' alignments in the T formation.
The formation begins with the usual 5 offensive linemen (2 offensive tackles, 2 guards, and a center), the quarterback under center, and two backs in-line behind the quarterback. The base variant adds a tight end to one side of the line and two wide receivers, one at each end of the line." [I formation. Wikipedia]
The American football positions diagram example "I Formation (Offense)" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Football solution from the Sport area of ConceptDraw Solution Park.

"In American football, the pro set or split backs formation is a formation that was commonly used as a "base" set by professional and amateur teams. The "pro set" formation featured a backfield that deployed two running backs aligned side-by-side instead of one in front of the other as in traditional I-formation sets. It was an outgrowth of the original, three running back T-formation, with the third back (one of the halfbacks) in the T becoming a permanent flanker, now referred to as a wide receiver. ...
A common variant of this formation removes the tight end and replaces it with a third receiver in the "slot" position. The formation is utilized to remove a defensive player from the tackle box to give the offense a 7-on-6 matchup.
There are three formations in the pro set of forms: Pro, Ace, and Tree." [Pro set. Wikipedia]
The American football positions diagram example "Pro set formation (Offense)" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Football solution from the Sport area of ConceptDraw Solution Park.

"In American football, a T formation (frequently called the full house formation in modern usage) is a formation used by the offensive team in which three running backs line up in a row about five yards behind the quarterback, forming the shape of a "T".
Numerous variations of the T formation have been developed, including the Power-T, where two tight ends are used, the Pro T, which uses one tight end and one wide receiver, or the Wing T, where one of the running backs (or wingback) lines up one step behind and to the side of the tight end. Any of these can be run using the original spacing, which produced a front of about seven yards, or the Split-T spacing, where the linemen were farther apart and the total length of the line was from 10-16 yards." [T formation. Wikipedia]
The American football positions diagram example "Offensive formation - T-formation" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Football solution from the Sport area of ConceptDraw Solution Park.

"The shotgun formation is a formation used by the offensive team in American and Canadian football. This formation is used mainly for passing plays, although some teams use it as their base formation. In the shotgun, instead of the quarterback receiving the snap from center at the line of scrimmage, he stands farther behind the line of scrimmage, often five to seven yards back. Sometimes the quarterback will have a back on one or both sides before the snap, while other times he will be the lone player in the backfield with everyone spread out as receivers." [Shotgun formation. Wikipedia]
The American football positions diagram example "Shotgun formation (Offense)" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Football solution from the Sport area of ConceptDraw Solution Park.