What it is

A cut block is a block at the legs. The blocker dives low to make the defender fall, often to stop him from reaching a ball carrier.

In a game

Cut blocks are common in zone-running plays. They are legal in certain situations but limited near the line of scrimmage.

More detail

The rules protect defenders from low blocks that come from behind, and a block that is too low or from the side can be a chop block or clipping. Cut blocks are dangerous, so the league watches them closely.