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. The NFL had previously outlawed blocks below the waist by players in change of possession situations and during kicks.
Cut blocks can also be used on split-zone blocks, which we, unfortunately, witnessed when Kayvon Thibodeaux hurt his MCL against the Bengals in the preseason. That, too, can be classified as a cut block and is perfectly legal.
A chop block is an illegal blocking technique where an offensive player goes below the waist of a defender while the defender is engaged with another offensive blocker up high. This is a 15-yard penalty.
There is also the low block, the peel-back block, and the crackback block.
A low block is only enforced on kicking or on change of possession plays - don’t cut on these punts, kickoffs, interceptions, or fumble recoveries. This is a 15-yard penalty.
The peel-back block prevents an offensive player from initiating contact on the side and below the waist of an opponent if the blocker is moving toward his own end line and if the initiator approaches the opponent from behind or from the side.
However, if the blocker’s near shoulder contacts the front of his opponent’s body, then the peel block is fair game. An illegal peel-back block is a 15-yard penalty.
An illegal crackback block occurs when an offensive player comes from more than two yards outside the offensive tackle, or from the backfield, and makes contact below the waist, above the neck, from a blind side, or from behind.