The offense has some great advantages in football. The offense dictates much of how the defense will line up (by determining the strong side of the field and where the eligible receivers are lined up), the offense dictates when the play starts, and the offense tries to dictate where the play will go. The New Orleans Saints do an excellent job of using their formations, alignments and personnel to force the defense into mismatches. They do this most commonly by passing out of running formations. The defense substitutes while the offense is in the huddle. They substitute based on who the offense has brought into the game and the down, yardage situation. If the defense sees the offense bring in a 4 wide receiver set, the defense will substitute their nickel package into the game to counteract that. When the offense keeps their running formation in the game, the defense has to leave their run stoppers (defensive tackles and linebackers) in the game, unless it is an obvious passing situation. If the offense can force the defense to keep players in the game that are less competent in pass coverage, they can create, and then exploit favorable matchups.
Here is an example of the New Orleans Saints creating, recognizing, and taking advantage of bad matchups. They use this play to get Reggie Bush and Pierre Thomas into space and allow them to use their speed to make plays. This is an I-formation RB Swing Pass.
As soon as Drew Brees gets to the line on this play, he knows he will be throwing the ball to running back Pierre Thomas. The defense is in a man cover 2 defense, with three linebackers in the game to stop the run. Both the cornerbacks are on the offense’s right side man-to-man with the receivers. There is an outside linebacker in man coverage on the tight-end and linebackers in man on both backs. The receivers on the right side of the formation are going to run a fly-post combination, mainly to clear out the sideline and take the safety down field. The right tackle will chip the defensive end, but will leave him basically unblocked. This leaves the right tackle free to get out into the flats and block the linebacker that is in man-to-man on Thomas. The matchup this play creates is putting a linebacker in a foot race to the sideline with a speed back like Pierre Thomas or Reggie Bush.
Here is what the play looks like when it develops. The defensive end is left unblocked (red circle), but gets big eyes and starts thinking sack, effectively running himself out of the play. The linebacker covering Thomas knows he is in a foot race with Thomas, so he takes off toward the sideline. Here Thomas was able to beat him to the sideline initially, but as the defender began to over pursue, Thomas cut right off the right tackle and set up a great block on the linebacker. Since the receivers had run off the safety and cornerbacks Thomas is able to run free for about 13 yards before anyone even gets close to him.
Throwing the ball out of traditionally run formations keeps the defense on its toes and allows the offense to take advantage of poor coverage players having to play the pass. If the offense is successful throwing out of these formations and the defense tries to substitute a more traditional pass package (nickel or dime defenses), the offense can audible and run the ball on a now much smaller defense.