If the season averages hold, it will only happen about 13 times on Saturday, but those 13 snaps could decide the game: LSU’s offense versus Alabama’s defense on third down.

A consistent critique of his own defense from UA coach Nick Saban is its performance on third down. No. 1 LSU will bring the nation’s sixth-best third-down offense (50.51 percent conversion rate) to Tuscaloosa for its showdown with No. 2 Alabama, presenting a matchup that will likely impact the outcome of the game. This season, SEC teams are 34-5 in games in which they convert 50 percent or more of their third downs.

On the other side, the UA defense ranks 40th in the nation, allowing opponents to convert 34.78 percent of their third downs. That number did get one percent better by facing Arkansas, ranked 112th in third-down offense. UA predictably shut down the Razorbacks to three conversions in 12 attempts.

Earlier in the season, when Saban was discussing third-down defense as a way of getting the unit off the field, a look at the numbers showed the distance to go was as big a factor as the execution on that down. UA was facing far too many third-and-shorts to expect to be as good on third down as it has been in the past (top 25 in two of the last four seasons), and that remains the case.

Of the 114 third downs UA has faced, 57 of them (50 percent) have come with five or fewer yards to gain; 36 of them (31.5 percent) have come with three of fewer yards to gain. As expected, UA is allowing more conversions in short-yardage than otherwise: when facing third and five or shorter, UA is allowing a conversion 56.1 percent of the time, compared to just 14 percent conversions on all other third downs.

“I think it’s a combination of creating the right down and distance for yourself on third down, which obviously if they get you in third and short, they have a better chance to make it,” Saban said. “I also think we’ve had a couple of penalties on third down, which have extended drives, pass interference or whatever it might be. But I do think that we need to do a better job of executing, whether it’s a pressure or a coverage.

“We’re close a lot of the times but we need to make the plays.”

Now it faces an LSU offense that has shown it can convert on the critical down.

Part of LSU’s offensive success to date is that it has not faced third downs all that often — only 10 teams in FBS have fewer than LSU’s 99 third-down attempts — but when the Tigers get there, they convert.

The same offensive changes that have LSU at the top of college football are the same ones that will make them a tough task on third down.

“They’re a completely different scheme. They’ve been in empty like at least 80 percent of the time probably on third down,” Saban said. Empty is when there is no running back in the back field, often resulting in five-wide receiver sets.

“They like to see what you’re in and then try to take advantage of it however best they can relative to the quarterback kind of knowing what you’re in or them getting the best play call versus what you’re in. They’ve been very effective in making the defense declare itself so they can see what you’re in and then doing a good job of executing and taking advantage of it.”

Reach Brett Hudson at 205-722-0196 or bhudson@tuscaloosanews.com or via Twitter, @brett_hudson