Under NFL, NCAA, and NFHS rules, there are actually two lines of scrimmage at the outset of each play: one that restricts the offense and one that restricts the defense.
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(In 1994, that reference to the line of scrimmage was changed to the kick spot, which is usually 7 yards behind the line of scrimmage.) Notice that the 20-yard line is where the defense takes possession after a touchback.
With the #5 Aggies trailing Texas Tech 17-16 with time running out in the fourth quarter on a third-and-long play, quarterback Jeff Granger broke away from Tech's Dusty Beavers to avoid a sack deep behind the line of scrimmage.
Washington Redskins coach Joe Gibbs first began using the single-back as a base offense in order to move defenders off the line of scrimmage.