Indiana football, Tom Allen’s 4-2-5 defense and Jeff Brohm

Indiana football’s game against Louisville on Saturday will bring head coach Tom Allen face-to-face with a familiar foe: Jeff Brohm.

Not that there’s any bad blood there I’m sure the two are on amicable terms but Brohm had Allen’s number throughout the former’s tenure coaching the Boilermakers in West Lafayette. Allen’s Indiana beat Brohm’s Purdue once, in 2019.

Most of these games were close, Brohm won by a touchdown in 2017 and 2018, lost by three in 2019, then proceeded won by multiple scores the next two years as Purdue reached its peak under his watch. Now he’s back home in Louisville where Cardinals fans are more energized than they’ve been in years.

So, what made the matchup so lopsided?

Brohm was an offensive coach while Allen was a defensive coach, having been promoted to the head coaching gig after working as the team’s defensive coordinator with a background in the state.

Allen runs the 4-2-5 defensive system in Bloomington and has throughout his tenure. The system consists of, per its name, four down linemen, two linebackers and five defensive backs. This system allows Allen to have six defenders in the box a majority of the time while having, in theory, the defensive backs to account for the passing game.

For a more in-depth look at Allen’s 4-2-5 system, check out this writeup and this film review over at Bite-Sized Bison.

This defense has produced multiple high-caliber linebackers out of Bloomington such as Tegray Scales, Micah McFadden, Cam Jones and now Aaron Casey. Allen can deploy these linebackers in blitz packages while rushing four linemen.

Its weakness lies in that it’s not a “mirror” defense. One side of the field is always going to have less coverage and be more exposed as a result. That, combined with some space in the middle, can lead to some big plays.

Big plays are Jeff Brohm’s bread and butter. His offenses excel at getting the ball to the best players, as he did at Purdue with players like Rondale Moore and Charlie Jones. He was frequently able to generate explosion against Allen’s defense.

Louisville has some playmakers in year one of the Brohm era. Jamari Thrash was one of the better receivers in the country at Georgia State and Kevin Coleman has plenty of speed. The Cardinals have scored 39 and 56 points in their first two games of 2023, he has pieces to work with.

Brohm has to rely on former Purdue and Cal quarterback Jack Plummer to get his talent the ball though, and he threw one pick against Georgia Tech before tossing two to Murray State. And yet, 56 points against the latter.

Plummer will need to be decisive and accurate against an aggressive defense that thrives on takeaways. If Louisville can minimize mistakes and get the ball where it needs to go, Indiana will be in trouble.

Additionally, Indiana has a new play-caller for the scheme this year in Matt Guerrieri, who learned from Ohio State defensive coordinator Jim Knowles in Columbus last year as he implemented his own 4-2-5 system with Allen.

We’ll see how it all plays out on Saturday, but this isn’t Brohm’s first go around with Indiana’s defense.