A term for a moment when a defense denies a running play at the line of scrimmage. Specifically, a stuff refers to when an offensive team attempts a run up the middle that gets completely denied by the defense at or behind the line of scrimmage. Often, this play occurs on short yardage situations when both teams have jumbo packages in the game and are geared up to attack the middle of the line. The defense will achieve a stuff by bringing in extra defensive linemen and having them attack the center of the offensive line.
A stuff can be an exciting and game-changing play. Typically it means the defense managed to deny the offense a first down or touchdown, thereby swinging the momentum to its side. The best way to achieve it is to bring in a much larger defensive unit that has a better chance of overwhelming the offensive line. Since the risk of being stuffed can be great to certain offenses, the offense might combat this by using a misdirection play or play action pass to get the defense to commit to guarding the center while the offense actually runs a play to the outside. Sometimes this can lead to big plays for the offense.