For two and a half weeks, LSU’s defense was impenetrable. Tougher to crack than a diamond, and harder to find a hole in than the Fortress of Solitude. That changed last Saturday, when Mississippi State found the weak spot on the Tigers’ D and tore it wide open.

It seems like forever ago, but LSU couldn’t stop the run in the first half of their opener against Wisconsin. Melvin Gordon was running roughshod through the heart of the defense, picking up chunks of yards with every carry. On the first play of the second half, he ripped off a 63-yard run, and Wisconsin pounded the ball in a few plays later. From that point until the start of the Mississippi State game, LSU’s defense was airtight.

But the problem that Wisconsin uncovered early and lost sight of late didn’t go away, it was just glossed over by dominating performances elsewhere on the defensive unit. The pass rush got rolling against offenses that had to throw the ball, linebackers swarmed to ball carriers, the secondary gave receivers no room to breathe.

None of those things mattered against Mississippi State as the Bulldogs took it right at the Tigers’ defensive tackles, that one glaring hole. All season, Les Miles and John Chavis had been rotating three players at the position, with reserves getting a small percentage of snaps. Outside of Quentin Thomas (already playing through a biceps injury), Christian LaCouture and Davon Godchaux, LSU wasn’t getting production from anyone else.

Now, that lack of depth is rearing its head. Frank Herron and Greg Gilmore, both redshirt freshmen, didn’t get on the field against Mississippi State and Marquedius Bain, another redshirt frosh, didn’t make an impact. Now that Thomas is out for “a week or two,” LSU’s defense needs answers, and fast.

Miles and Chavis have experimented with moving two defensive ends, Danielle Hunter and Lewis Neal, into the middle. Miles praised Neal in his Monday press conference, but the sophomore is only listed at 255 pounds, while Hunter’s speed and size make him a better fit on the outside.

Every year, it seems one of the biggest knocks on the Tigers is their youth in critical spots. Often, they’re able to overcome that thanks to their sheer talent level, but it’s hurting them this year. Herron and Gilmore have both struggled for field time due to their inability to get up to speed on game plans. As both guys have a year in the program already under their belts, that’s an issue.

It’s expounded more when you look at LSU’s upcoming schedule. In two weeks, the Tigers head to Auburn to take on one of the country’s strongest rushing attacks. Gus Malzahn will most likely be on the Plains licking his lips thinking about how many yards per carry his Tigers can average on Oct. 4. In November, LSU faces Alabama at home and goes on the road to Arkansas in back-to-back weeks, two more teams that can run the ball and bulldoze defensive lines with the very best of them.

In the mean time, the Tigers have two weeks to shore up their defense before Auburn. A loss there would more or less end any chance LSU has at winning the brutal SEC West. Fixing those issues will have to start this week against New Mexico State, with the redshirt freshmen getting on the field at defensive tackle and proving they can handle a real workload.

The Tigers’ season might depend on it.