In gridiron football, blocking below the waist is an illegal block, from any direction, below the waist by any defensive player or by an offensive player under certain situations, by any player after change of possession, by any player in high school with certain exceptions. It is sometimes incorrectly referred to as a "chop block". Such blocks are banned due to the risk of injury, particularly those to the knee and ankle. The penalty for a block below the waist is 15 yards in the NFL, NCAA, and in high school. The block is illegal unless it is against the ball carrier.