MIKE Ja'Whaun Bentley is a stout run defender.

Purdue's rapid ascent from basement dweller to upset threat in their first season under Jeff Brohm has been the story of the Big Ten so far. While the much-improved (and far more entertaining) offense has received most of the attention, the defense has also taken a step forward under new defensive coordinator Nick Holt (Nick Holt!), who followed Brohm from Western Kentucky to Purdue and is transitioning the defense from a 4-3 to a 3-4.

It was tough to pick a game to break down for this post. Mizzou, last weekend's opponent, fired their defensive coordinator before losing 35-3. Ohio, the previous week's opponent, couldn't stay close for long and ranks #89 in S&P+. That leaves Louisville, the opponent closest in talent, albeit not style, to Michigan. Purdue put a serious scare in the Cardinals in week one, losing 35-28, and while the final score was a bit fluky—based on his numbers Bill Connelly gave Purdue an 11% win expectancy—the game showed the Boilermakers can hang with more talented teams.

About that flukiness, though. Louisville coughed up two fumbles at Purdue's goal line (and lost a third early in another drive) to keep this one closer than it should've been. A summary of UL's drives:

• 8 plays, 52 yards, fumble at PU 2
• 8 plays, 64 yards, touchdown
• 10 plays, 75 yards, touchdown
• 6 plays, 75 yards, touchdown
• 10 plays, 72 yards, field goal
• 9 plays, 46 yards, field goal
• 6 plays, 14 yards, fumble at PU 1 (drive set up by PU fumble on kickoff return)
• 4 plays, 17 yards, punt
• 4 plays, 7 yards, field goal (drive set up by long punt return)
• 2 plays, 16 yards, fumble
• 3 3-and-outs

Six of Louisville's 13 drives covered at least 45 yards, they were a yard short of a touchdown on a seventh drive, and a fumble after a completion cost them a chance at another score. Purdue was fiesty, and their linebackers made some impressive plays, but they've still got some issues to work out, particularly on the back end.

Personnel: Seth's diagram [click to embiggen]:

As explained in more detail below, Purdue shows multiple fronts but mostly plays with three down linemen.

Base Set? Multiple. Purdue's depth chart lists 4-3 personnel, though when they line up in a four-man front it's usually with a standup weakside end—think DJ Durkin's BUCK. For the most part, however, they lined up in a 3-4 or 3-3-5, using DE Danny Ezechukwu as a rush linebacker and backup safety Navon Mosley as their extra defensive back. They'll usually have the outside linebackers flanking the DEs, like so:

They'll line up in more of a stack, usually on passing downs:

[Hit THE JUMP for the rest of the breakdown.]

Man or zone coverage? Purdue mostly played zone, switching between Cover 2 and Cover 3. They were susceptible through the air, especially over the middle and up the seam.

Pressure: GERG or Greg? The presence of reigning Heisman winner Lamar Jackson, a superb scrambler, certainly affected how Purdue approached rushing the passer. While they mostly sat back on early downs, they tended to bring an extra rusher or two on third downs; they needed to, as the defensive line generated no pressure on their own. While that was in part due to maintaining lane discipline against Jackson, Purdue has only one sack all season.

Dangerman: At 6'2", 260, MIKE Ja'Whaun Bentley looks like a defensive end at first glance, and he brings the wood against the run. He had seven TFLs last year despite missing three games to injury; so far this season he leads the team in tackles and has recorded two TFLs, five run stuffs, and two forced fumbles.

While he's not the most nimble athlete, which shows up when he drops into zone coverage, he diagnoses plays quickly and takes good angles to the ball—he always seems to end up in the pile. His goal line forced fumble against Louisville was a thing of beauty; watch #4 read the play in an instant, get to the hole with leverage, and stop the back cold in his tracks while knocking the ball free:

He's the best of a solid group of linebackers despite some issues in coverage. With Bentley's size, strengths, and weaknesses, the comparison to Mike McCray is pretty tight. Because he plays inside in a 3-4, Bentley isn't asked to make plays in space as often as McCray, so his shortcomings are more mitigated by scheme.

Up front, a familar name stands out. 6'1, 280-pound end Gelen Robinson is Glenn Robinson III's younger brother, though a "Little Big Dog" moniker could only be used ironically. Gelen's strength is also against the run; he had one of the plays of the Louisville game when he two-sided a block, shed, and tackled Lamar Jackson short of the sticks on a third-and-three:

While he's not an impactful pass-rusher, he showed some active hands, tipping a pass at the line to get another third-down stop. He can get pushed around some by down blocks and double-teams, but for the most part it's best to run to the other side.

OVERVIEW

The move from a 4-3 to a 3-4 mostly works with this personnel, though there's an awkward fit or two. Nose tackle, in particular, seems better suited to a four-man line. Co-starter Eddy Wilson is undersized for a zero- or one-tech at 295 pounds, but he's better than 325-pounder Lorenzo Neal, the other co-starter. Neal is a pretty uninspiring space-eater, while Wilson at least threatens the backfield on occasion, though that does mean he'll sometimes get blown out of a gap. Robinson is stout on one end, but the other is manned by another undersized player, 255-pound senior Austin Larkin.

That means Purdue doesn't stuff many runs at the line. Their linebackers, led by Bentley and sophomore spacebacker Markus Bailey, mitigate this issue by aggressively flowing to the ball. Even with Lamar Jackson making some spectacular plays, Louisville didn't have a run longer than 15 yards, and that was mostly due to the linebacker level. Bailey is the jack-of-all-trades; he'll play in the box, slide over the slot and cover, or blitz off the edge.

The other two linebackers were up-and-down. OLB Danny Ezechukwu is nominally their best pass-rusher, and while he can be disruptive, he's doesn't consistently generate pressure on his own. Inside linebacker TJ McCollum, a grad transfer from Western Kentucky, got out of his lane a couple times against the run and let himself get cut to the ground for the key block on UL's touchdown run:

That play is also an example of Robinson not always holding up in the run game.

Purdue almost exclusively played zone coverage, with the rare exceptions usually coming on heavy blitzes. The cornerbacks were solid on the outside; Louisville didn't test them much on the perimeter, and senior Da'Wan Hunte was step-for-step with his mark when UL tried to go deep on him. Louisville didn't need to go at him often, however, because the middle of the field was open for business. Slants were easy money and threatened to break big if the safeties missed tackles, like TJ Jallow does here:

The safeties generally appeared a beat late getting to intermediate and deep throws over the middle and up the seam. It didn't help that the linebackers didn't always get great depth in their drops, and the problems were exacerbated further when Purdue got predictable with their coverage; on this play, Louisville sends three vertical routes at the two deep safeties, who don't disguise the Cover 2 look at all, and splits them down the middle for a big gain:

Check back in after I cover the offense tomorrow, but after watching this game a couple times and focusing on the defense, I'm feeling less nervous about Saturday than I did heading in. While Purdue has some good players up front, they're not a complete defense against either the run or the pass. Michigan, of course, needs to work through some issues of their own on offense, but Purdue doesn't seem well-equipped to exploit one of the bigger problem spots—their lack of a pass-rush could take the pressure off Nolan Ulizio (and therefore Wilton Speight).