The roots of the 4-2-5 defense go back to the old 4-4 Split defense. Whereas the 44 Split had two inside linebackers and two outside linebackers, the 4-2-5 has two inside linebackers and two secondary players. The 4-2-5 replaces one OLB with a LB/safety hybrid, the nickelback. While using a fifth defensive back against pass-happy offenses isn’t new, the 4-2-5 made the nickel package the base defense. When facing an offensive running 12 personnel, the nickel defense reverts back to its 4-4 roots.
The nickelback is a de facto OLB when facing 12 personnel. The extra gaps created by two extra TEs on the offensive line mean the defense is not gap sound with four defensive linemen and two inside linebacker. The nickel back on one side and the cornerback on the opposite side fill those two extra gaps. The cornerback and nickelback mean the defense can hit its run fits when the offense goes to a heavy formation.
Nickel Defense Run Fits
The play diagram above shows the run fit adjustments when facing 12 personnel. The offensive alignment shows a TE and H-back aligned to the right, so the MLB has the strong C gap and the WLB has the weak B gap. The weakside edge takes the weak C gap, leaving the weakside CB responsible for any D-gap runs.
Nickel Defense Executes Vs 12 Personnel
Defensive line is DeMarvin Leal as SDE, McKinnley Jackson at 3-tech, Jayden Peevy at 1-tech, and Michael Clemons at WDE. Aaron Hansford is the MLB and Andre White is aligned at WLB. Nickelback Antonio Johnson is aligned to the field, he is the fourth LB or SOLB in a 4-4 on this play. Jaylon Jones is the WOLB responsible for the weak D-gap from his CB position.
At the snap, Auburn is running inside zone. The H-back goes in slice motion weakside and arc blocks around Clemons, who is the read man on this play. Clemons pinches down to fill the C-gap and force the keep read for QB Bo Nix. The slot receiver motions weakside and tries to block Jones outside. Jones leverages the slot receiver with his inside shoulder so he can keep his outside arm free and force Nix back inside. Clemons plays inside-out and pursues Nix from behind. Nix has nowhere to go between Jones and Clemons as they tackle him for a one yard gain.
Result of the play is a one yard gain setting up 3rd and 9.
