The cut block is a legal blocking technique that consists of an offensive player knocking a defensive player down by targeting his knees. Many believe this block is dirty, but it is legal in certain situations. It can be exercised by blockers at the line of scrimmage when the defender is not engaged with anyone else.
In 2021, the NFL passed a new rule that proposed to penalize blocks below the waist by offensive and defensive players on scrimmage downs when contact occurs beyond five yards on either side of the line of scrimmage and more than two yards outside of either offensive tackle.