A cut block in football is a play in which an offensive line player tackles a defensive player below his waist in an attempt to knock him down, that way stopping him from getting to the ball carrier. Although very effective if done correctly, a cut block is considered by some people a rather dirty play as it usually strikes the defensive player's knees, a very sensitive and injury-prone area. Cut block plays are very common in the blitz to pick up and its variants.
Although cut blocks are legal both in the NFL and in College Football, a very similar play, the chop block, is not. Chop blocks are the same as cut blocks with the exception that two offensive players team up to cut block a defensive player. Because this type of block is illegal, it is necessary for football officials to be very attentive when those kinds of plays happen.
It takes a lot of speed, agility, and strength for a player to execute a cut block, and given that offensive players' main skills are not tackling, its technique has to be properly and thoroughly trained for it to be effective. Players try to hit the opponent's knees with their shoulders and then do a turning motion, knocking the defensive player down.