Activities Sports & Athletics Defensive Gap Control Numbering System Positions Players to Make Tackles Share PINTEREST Email Print David Madison / Getty Images Sports & Athletics Football Basics Playing & Coaching Best of Football Plays & Formations 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 April 04, 2017 While phrases such as "he's in a five-I," or "he lines up in a shade" are used matter-of-factly by ex-athletes announcing football games, those new to the sport (and even some long-time fans) may not fully understand these and other terms associated with the concept of gap control defense. Gap Description A gap is the area between each offensive lineman. The "A" gap is between the center and guard. The "B" gap is between the guard and tackle. The "C" gap is between the tackle and the tight end (or outside the tackle if no tight end). The "D" gap is the area outside the tight end. 1-Gap Defense The intent is to have each offensive gap occupied by a defender. Strategically placing a defender is the key to getting him past the opposing lineman, and covering or "securing" his gap assignment. Defensive Technique Numbering System The system created by O.A. "Bum Phillips," and made famous by Paul "Bear" Bryant decades ago, continues to be used by football coaches to correctly line up defenders. While gap lettering is helpful, the numbering system makes it easier for players to line up in a particular area designated by the coaches. Definition of Techniques "0" Tech - Instructs defender to align "head up" on the center. "1" Tech - Instructs defender to align his outside shoulder with the inside shoulder of the guard. "2" Tech - Instructs defender to align "head up" on the guard. "3" Tech - Instructs defender to align his inside shoulder with the outside shoulder of the guard. "4" Tech - Instructs defender to align outside shoulder with the inside shoulder of the tackle. "5" Tech - Instructs defender to align inside shoulder with the outside shoulder of the tackle. "7" Tech - Instructs defender to align outside shoulder with the inside shoulder of the tight end. If no tight end, defender aligns on the imaginary tight end. "6" Tech - Instructs defender to align "head up" on the tight end. "9" Tech - Instructs defender to align inside shoulder on the outside shoulder of the tight end. Technique Tweaks Adding i to a technique instructs the player to move slightly inside. A "5i," for instance, instructs the defender to align slightly inside the outside shoulder of the tackle. Think of it as the defender's inside eye "head up" on the offensive tackle's outside eye. Adding Shade to a technique is another way to move a player slightly toward a particular gap. ("0" Shade would instruct the nose tackle to adjust slightly toward a gap, e.g.) Offenses Reference Numbering System Offensive coaches teach linemen and quarterbacks to recognize the alignment of the defense. Example: A team running the midline, or inside, option play. Facing a defensive alignment with a "3" tech to one side and a "1" tech to the other, the quarterback will run the play toward the "3" tech defender as the alignment creates a better advantage for the blockers.