Activities Sports & Athletics Simplifying Over/Under Defensive Football Calls Defensive Line Spacing in the 4-3 System Share PINTEREST Email Print David Madison/Getty Images Sports & Athletics Football Plays & Formations Basics Playing & Coaching Best of Football College Football Baseball Basketball Bicycling Billiards Bodybuilding Bowling Boxing Car Racing Cheerleading Cricket Extreme Sports Golf Gymnastics Ice Hockey Martial Arts Professional Wrestling Skateboarding Skating Paintball Soccer Swimming & Diving Table Tennis Tennis Track & Field Volleyball Other Activities Learn More By Sean McCormick Updated October 05, 2018 Football teams either run a 3-4 defense or a 4-3 defense, with the numbers referring to down linemen positioned at the line of scrimmage (the first number) and the number of linebackers behind them (the second number). Each system has its benefits and challenges, but teams using the 4-3 defensive system will benefit from mastering both the Over and the Under front line spacing alignments. Over Alignment The term Over is used to describe any defensive front where the strong side defensive tackle will take a "3" technique position opposite the strong side offensive guard. The back side defensive tackle will move over toward the strong side and position himself in a "1" technique. Under Alignment The term Under describes any defensive front where the strong side defensive tackle is aligned in a "1" technique over the strong side guard, while the back side defensive tackle takes a "3" technique position across from the offensive guard. Linebacker Adjustments When there is a tight end, regardless of whether it's an over or an under call, the strong side outside linebacker (Sam) will move to the line of scrimmage to the tight end's outside shoulder. The positioning of the back side outside linebacker (Will) and the middle linebacker (Mike) will vary with the over or under call, whether or not a specific blitz is called, and what formation the offense is using. Coaching Points When aligned in the Under front, teams need to be aware of the potential problem the offense can create if a running back can be successful at surging into the back side A-gap. The Over/Under front can also be attacked by a midline option team, as the quarterback will determine the side of the midline call according to the spacing of the defense tackles. Defenses successful with 4-3 formation take advantage of the multiple blitzing and pass coverage schemes provided by the Over/Under fronts.