TUSCALOOSA – Brian Kelly put up three key adjustments on the whiteboard for his defense at halftime.

1. Better eye-discipline

2. Better leveraging

3. Better tackling

They were sound adjustments for his defense. LSU football (6-3, 4-2 SEC) had surrendered 295 yards and 125 rushing yards in the first half to Alabama (8-1, 6-0), an offense that had yet to accumulate more than 415 yards of offense against an SEC team this season.

Kelly knew what LSU's problem was, the same problem that has haunted the Tigers all year: their defense.

And yet, Kelly didn't fix it, at all.

The Tigers lost to Alabama on Saturday, 42-28. They allowed 507 yards and couldn't get off the field on 11 of 14 third down opportunities. They surrendered 288 rushing yards, gave up touchdowns every time the Crimson Tide got into the red zone and allowed an average of 14.6 yards per completion.

Adding insult to injury, their tackling only worsened after halftime. Their eye discipline and leveraging failed to improve as well.

"None of those three things showed up to be better than good," Kelly said after the loss.

But where is the disconnect? How can a unit with former five-star recruits and top transfers play this poorly on defense?

"I think in the second half, a lot of guys were just not doing their jobs," linebacker Greg Penn said. "I think fatigue set in for the defense, staying on the field for a long time.

"I think those were the key factors."

A big part of the problem for LSU's defense on Saturday, despite its talent, was injuries and absences. The Tigers were without the four cornerbacks they added from the transfer portal, top defensive lineman Mekhi Wingo and safety Greg Brooks Jr., their captain.

Those absences, especially at cornerback, forced the Tigers to drop extra bodies into coverage, allowing Alabama quarterback Jalen Milroe to scramble and run wild. Kelly said after the game that he thought LSU would have been shorthanded in coverage if it assigned a spy on Milroe.

Milroe had a team-high 155 rushing yards and four rushing touchdowns.

"I think it's the challenge that we knew, his ability to run," Kelly said. "We talked all week about a unit pass rush; he's elusive.

"I think for the most part, I think the big runs were probably the things that hurt us the most in that game."

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But Saturday wasn't just because of LSU's injuries and absences. Its tackling was unacceptably poor, a problem that has plagued the Tigers all year.

They were undisciplined and failed to zero-in on doing their own jobs. Instead of focusing what they needed to do, they were trying to do others' responsibilities as well as their own.

That was also a problem against Florida State and Ole Miss.

"I think sometimes guys over-pursuit and not trust the guy next to (them)," Penn said. "Like, this guy has to set the edge, let them set the edge if you stay inside out."

The definition of insanity is making the same mistake over and over again, only to expect a different result.

LSU knows what its problems are on defense. But its fans are losing their sanity watching them, if they haven't lost it already.

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Koki Riley covers LSU sports for The Daily Advertiser. Email him at kriley@theadvertiser.com and follow him on Twitter at @KokiRiley

This article originally appeared on Lafayette Daily Advertiser: LSU football: Why Brian Kelly can't fix the Tigers' defense