In a usual three-level defense, there are three layers: the forcing unit (consisting mainly of linemen but possibly also including shooting linebackers and defensive backs), the underneath coverage (usually consisting of linebackers but possibly including other players, especially in the case of a zone blitz), and the contain unit (mostly defensive backs). A two-level defense does away with the contain unit in favor of increased pressure on the offense. Two-level defenses will often use one deep safety (as deep as 28 yards at the snap) to enforce an end line on the offense, but the Bear 4-6 is a two level defense with contain handled solely by the single coverage skills of the cornerbacks. The "Bear" can also function as a three-level defense, and indeed concealment of the defensive struct