The tackle box is the width of the offensive line.
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Most spatial elements of a football field are clearly marked with chalk, paint or portable markers so that players, officials and fans can easily follow the action. A few elements, though, are not marked at all. For example, the tackle box in the NFL cannot be marked, even with portable markers, because the dimensions and orientation of the space vary from play to play. The dimensions of the tackle box follow a few basic rules determined by the alignment of the offensive line, and those dimensions impact several aspects of game play.
Tackle Box Basics
Even though football is a game of specific inches, there are no fixed dimensions for the tackle box. This is because it changes from play to play and depends on the relative size of the offense's personnel. The tackle box is a space that spans the length of the offense line, from the left tackle to the right tackle. It extends from the line of scrimmage to the goal line behind the offense. The location of the tackle box depends on where the line of scrimmage is for a given play, as well as where on that line the ball is marked for the snap.
The dimensions of the tackle box dictate much of what the offense can and cannot do during a play. For example, the quarterback must either cleanly hand off, pitch, pass or run with the ball while he is standing within the tackle box. The dimensions of the tackle box are set as soon as the ball is snapped, meaning that the offensive line cannot extend or contract themselves laterally while the play is in motion to increase or decrease the size of the tackle box.
While the dimensions of the tackle box are determined by the alignment of the offensive line, the defense is also constrained by rule while the quarterback is within the box. For example, while the quarterback stands in the pocket within the tackle box, defenders cannot dive at his legs or tackle high aiming for the head. All contact with the quarterback must be above the knee and below the neck, unless the quarterback has stepped beyond the tackle box and then re-entered that space while scrambling. Once the quarterback exits the tackle box, most of the rules governing it no longer apply for the rest of the play.
The most prominent aspect of play that the dimensions of the tackle box govern is intentional grounding. While standing within the tackle box, the quarterback cannot throw the ball out of bounds or to the ground without an eligible receiver nearby. Intentional grounding will result in a loss of the down, a loss of 10 yards from the previous spot of the ball, or, if the quarterback was standing more than 10 yards from the line of scrimmage, wherever the pass was made from. If the quarterback stands in his own end zone, intentional grounding will result in a safety penalty, and two points will be awarded to the opposing team. As long as the quarterback moves laterally out of the tackle box, then throws the ball at least to the line of scrimmage, intentional grounding does not apply.