also: cut · low block
A block below the waist intended to take a defender off his feet.
A blocker attacks below the waist instead of trying to drive the defender upright. This often requires the offensive player to dive at the defender's legs in an attempt to knock him over.
Rules around cut blocks vary from league to league. High school rules can vary by state. College football and the NFL allow cut blocks only under certain circumstances and have banned them outside the tackle box. You may still see a running back throw his body at a blitzing linebacker during pass protection.
A cut block uses one blocker. A chop block combines a low block with a second blocker engaging the same defender high.
low blockchop block