also: pin block · pinning
Sealing a defender to the inside so the play can get around him. Half of pin and pull, and a word coaches also use loosely for any block that traps a man where he stands.
To pin is to block a defender inward and keep him there, so that the play can get outside him. It is a down block whose success is measured by the defender not getting back out rather than by how far he was moved.
It is the block half of pin and pull: covered linemen pin the men on them while uncovered linemen pull around, which is how a scheme gets pullers without giving up the interior.
pin him insidedown block, sealPin and down block describe the same movement and are not fully interchangeable. Down names the direction; pin names the direction plus the requirement that he stay there. A coach will use them loosely and mean the same thing most of the time.