Breaking down what went wrong for Alabama in Nick Chubb's touchdown run

Alabama's defense was near-perfect on Saturday, largely silencing one of the best running backs in the country in Georgia's Nick Chubb. The stat sheet won’t tell you that, though, listing Chubb at 146 yards on 20 carries. Most of those yards, however, came on on 83-yard touchdown run given up in the third quarter. Alabama coach Nick Saban praised his defense but was clearly discontent with the play, mentioning it several times in the course of his postgame press conference.

“I was really pleased with the way our backers played,” Saban said. “Now, we got in the wrong gaps. The players got a little bit confused. We were basically playing two different fronts: one’s an ‘odd’ front and one’s an ‘even’ front. The calls we make on an ‘odd’ front changes gaps for guys. But we were in an even front and Reuben thought he was in an ‘odd’-front gap. The ball spit and the secondary was keyed someplace else, and that’s why there was nobody there. Other than that play, they did a fabulous job.”

On the surface, this makes sense: linebacker Reuben Foster wasn’t where he needed to be on the play. But let’s dive into some of the details to see what really happened.

Like Saban said, Alabama is in an “even” front here. Basically, that means the two defensive tackles are lined up over Georgia’s guards, instead of lined up over center. Now, with Nick Saban’s defense, the front is never really playing a one-gap or two-gap defense all the way across. (If you’re not sure what that means, here’s a good breakdown from The Phinsider, SBNation’s Miami Dolphins blog). For simplicity’s sake, we’ll say that in this “even” front, Alabama should be playing a one-gap technique. The defensive tackles are responsible for the B-gaps, between the offensive guards and tackles and the ends are responsible for the C-gaps, over the outside shoulder of the tackles. For our purposes, left and right will always be from the perspective of the offense, so keep that in mind.

For Da’Shawn Hand, the defensive end closest to the camera, that means working against the tight end. For the far defensive end, actually linebacker Denzel Devall playing with his hand in the dirt, that means working against the right tackle. The center and right guard will double team Jarran Reed, and the left tackle and left guard will double team Dalvin Tomlinson. Effectively, that seals the left B-gap, the right A-gap and both C-gaps. (NOTE: Hand, particularly, is playing a kind of two-gap here, so it’s more complex than that, but this works for our purposes.)

This is where things go wrong for Alabama.

Ragland is responsible for both spelling the C-Gap over Hand’s left shoulder and the D-gap, or the outside edge, in case of a zone read. The possibility of a zone-read quarterback keeper, or Chubb cutting back to the edge, freezes him on the outside.

Safety Geno Mathias-Smith is correctly reading the play and crashing the right B-gap, which opens up wide. This is when Foster gets in the wrong gap.

Foster is playing both the A and B gap at the start of this play, and for some reason, moves into the B-gap, right in front of Mathias-Smith. That leaves the A-gap over the center’s left shoulder, where he should be, wide open for Chubb to barrel through.

Seconds later, Chubb was in the end zone and had booked his 13th consecutive game with 100-plus rushing yards, equalling a UGA record held by Herschel Walker.

The good news for Alabama fans is that this seems like an anomaly (this season, at least). Most advanced statistics have the Alabama rush defense well above the FBS average in limiting explosive plays, and this was more a mistake of execution than technique, and one that happened in the midst of a downpour in an unfriendly atmosphere. Alabama’s toughest road environment this season will likely be an expanded Kyle Field, and the Aggies, despite their offensive fire power, don’t have a Nick Chubb.

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