In the terminology of American football, clipping refers to a dangerous and strictly prohibited block executed when a player dives or runs into the back of an opponent—other than the immediate ball carrier—below the waist. Because defensive players and unsuspecting blockers cannot see a blow coming from behind, clipping carries a high risk of severe knee and ankle injuries, prompting officiating crews to enforce severe rules against the practice. When a clipping foul is flagged by referees, it results in a major fifteen-yard penalty assessed from the spot of the foul or the previous line of scrimmage, making it one of the most heavily penalized and scrutinized blocking infractions in the sport.