also: covering down · cover down to number two
Whether a defender can align to a slot receiver well enough to handle him. The answer decides how many defenders are left for the run.
The alignment relationship between an outside linebacker or overhang and the slot receiver in front of him: how far out and how deep he has to be to take that receiver's vertical release seriously. Being able to cover down is what frees a safety to come toward the box, so the phrase is really about the run game even though it describes a coverage alignment.
covering downCover 2, Cover 3, Cover 4 as numbers, apex