re: Ellis Johnson to Auburn, per source...

Bleacher report warning! but someone posted this on Rivals to explain his scheme.

LINK

The base formation can mostly simply be called a 4-2-5 defense. That is, four down linemen, 2 linebackers, and 5 defensive backs. Normally this would be called a nickel formation, but for reasons we will see, this isn't really a nickel defense.

The primary difference is that the fifth defensive back is more of a linebacker/strong safety hybrid than a typical nickel back. In a typical nickel scheme, the extra defensive back either plays a deep zone or covers the slot receiver one-on-one. In Ellis Johnson's scheme, the "spur" plays much more of a run-support/blitzing/underneath-coverage role than a nickel back.

So, in many ways you could call this defense a 4-2-1-4 defense: four down linemen, two linebackers, one spur, and four true defensive backs.