The chop block is usually considered illegal and penalized by a loss of 15-yards due to the injury risk it presents to the defender.
[1] Since the 2016 season In the National Football League (NFL), a chop block is an illegal move, penalized by a 15-yard loss.
It was considered legal on running plays when (i) the blockers were aligned next to each other on the line of scrimmage, (ii) the blockers were lined up anywhere on the line and the flow of the play is towards the block or (iii) the cut blocker was aligned in the backfield and the chop block took place outside the original tight end position.
[4] The cut blocker is said to "chop" the defender and usually engages simultaneously with or immediately after the high block.
[6] Although there were many variations and reforms made to the chop block technique, it was finally deemed illegal prior to the 2016–2017 season in the NFL, mainly due to the high probability of athlete injury.