The 3–4 defense which evolved from the old 5-2 defense has gained popularity since the seventies due to the present day spread formations and the passing game which renewed its use by modern professional and college football teams. The 3–4 defense is so named because it involves 3 down linemen and 4 linebackers. There are usually 4 defensive backs.
One basic approach using the 3-4 scheme is the ability to get lined up versus spread offensive formations and the ability to drop eight defenders into coverage while only rushing three defenders. When only rushing three defenders you are primarily wanting to contain the quarterback
allowing eight cover defenders to occupy all throwing lanes.
Typically, there are two major variations of the 3–4 defense. Both variations are directly related to coverage schemes on obvious passing downs. For the first type, the outside linebackers (inverts or over hang players) will rush the quarterback, the great majority of the time. On key situations, the rush linebacker will be sent to cover the flat on the opposite side of the blitzing defensive back; this is known as a “zone blitz”. This scheme requires outside linebackers to have the ability to back pedal and drop into coverage, of course they do rush the passer at times, it is just that they are much more likely to drop into coverage.
