In football, a low block is a block that is below the knees, both from the front and the back. A low block is an illegal block due to the extreme risk of injury the block provides. The low block is very similar to that of the cut block, wherein a lower body block is performed. Cut blocks and low blocks are often considered dirty plays due to the nature of the blocks. Performing a low block will result in a 15 yard penalty against the offending team.
If a player makes contact with a player above the waist and then moves below the waist, this does not count as a low block. A low block is only if contact is made below the waist first. The legality of the block depends on the player and where it is on the field. Sometimes, referees can miss a low block depending on their perspective on the field.
The low block can completely flip a player upside down and cause head injuries. It is an illegal block because of the dangers to the head, neck and shoulders.