The side of the ball that doesn’t feature the headliner battle could end up deciding it.

It was the defining game of the first half of 2016. Clemson leaped to a 28-10 halftime lead over Louisville in Death Valley last October, then Louisville scored 26 unanswered to take an eight-point lead. Clemson scored twice in four minutes to take the lead back, and with less than a minute left, Louisville and Lamar Jackson ran out of magic, coming up short on fourth down at the Clemson 3.

From that game emerged both a title contender (Clemson would finish the deal three months later) and a Heisman contender (Jackson took home the trophy two months later). Clemson needed big contributions from all of its stars — Deshaun Watson (306 passing yards, 91 rushing yards), Wayne Gallman (110 rushing yards), Ben Boulware (three TFLs and a fumble recovery), etc. — to survive at home.

Nearly a year later, the Tigers have to go to Louisville. So what's changed in the previous 50 weeks or so?

1. It's been pretty easy to get a still vibe thus far in 2017.

Jackson is still Jackson . In two games, he's thrown for 771 yards and rushed for 246 (not including two sacks). He's completing 65 percent of his passes, and half of his rushes have gained at least five yards. With a rather new skill corps around him, he’s still led the Cardinals to 41 points and 615 yards per game against two power conference defenses.

. In two games, he's thrown for 771 yards and rushed for 246 (not including two sacks). He's completing 65 percent of his passes, and half of his rushes have gained at least five yards. With a rather new skill corps around him, he’s still led the Cardinals to 41 points and 615 yards per game against two power conference defenses. Clemson's defense is still Clemson's defense. The Tigers sacked Auburn's Jarrett Stidham 11 times in a 14-6 win last Saturday, and they are combining epic front-seven aggression with impeccable big-play prevention; in two games, they've allowed one gain of 20-plus yards. Austin Bryant alone has more sacks (four) than 59 FBS teams. Including sacks, Auburn gained just seven net yards in 35 pass attempts. Seven.

That’s the obvious marquee battle.

Plenty of things have changed, however. And for all the familiar faces, the changes will likely decide Saturday night’s battle in the Bluegrass State.

2. Louisville's defense is laboring

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We're in a strange spot, talking about the Cardinals' defense: we don't know how good either Purdue's or North Carolina's offenses are. Purdue has showed high-octane moments in Jeff Brohm's first season, and UNC split between two new quarterbacks (redshirt freshman Chazz Surratt and grad transfer Brandon Harris) in Week 2, both of whom could turn out to be quite good in Larry Fedora’s offense. Or maybe they just looked good against Louisville.

Here's what we do know:

The Cardinals had to replace three of their best defensive players (linebacker Keith Kelsey and Devonte Fields and safety Josh Harvey-Clemons).

They traded defensive coordinators with Mississippi State, and in terms of track record, they got the shorter end of the stick. They lost Todd Grantham, who has a history of top-30 defenses, and got Peter Sirmon, who is regarded as a good recruiter but oversaw an MSU defense that fell to 73rd in Def. S&P+ last year.

They are thus far 110th in success rate allowed, 102nd rushing and 110th passing (though opponents have thrown far more than they've run so far). Purdue and UNC combined to complete 65 percent of their passes.

The run defense's grade is incomplete. The success rate is bad, but Purdue's top two backs still gained only 54 yards in 12 carries while UNC's gained just 38 in 14. It's hard to be too critical about that.

Still, the pass defense might struggle against a Clemson offense that isn't too aggressive but is completing 69 percent of its passes.

3. Clemson’s offense is not exactly in fifth gear either

Kelly Bryant

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It's equally difficult to get a read on Clemson's offensive capabilities. Thus far the Tigers have torched an outmanned Kent State and been mostly shut down by an awesome Auburn D.

Offensive co-coordinators Tony Elliott and Jeff Scott have been in "keep your new starting QB out of trouble" mode, and Clemson has been run-heavy with random doses of quick passing.

Against AU, Clemson gained 172 of its 281 yards on two drives — the last one of the second quarter and the first one of the third. Bryant threw nearly half his passes in that span.

In those two drives, quarterback Kelly Bryant completed 10 of 14 passes for 130 yards and rushed four times for 36 yards and a touchdown. The rest of the game, he was 9-for-15 for 51 yards passing (with four sacks for minus-25 yards) with 11 non-sack rushes for 18 yards.

Auburn’s secondary is sticky and experienced, and Clemson receivers Hunter Renfrow, Ray-Ray McCloud, and Deon Cain struggled to find separation. Even on the team’s two successful drives, there were minimal yards after catch, and the Clemson offense was limited mostly to quick passes near or between the hashes, lobs down the sideline, and zone-read keepers. McCloud (twice) and Cain (once) each caught lobs in traffic for big gains on the TD drives, but the big plays were minimal overall.

If Clemson has an edge on offense, it might simply come from the fact that Louisville’s secondary isn’t as good as Auburn’s. Even if most of the passes didn’t travel very far, Bryant still completed 66 percent of his passes against AU, and UNC went 29-for-38 throwing a lot of the same quick, easy passes.

4. S&P+ projects a 29-26 Clemson win, right at the Vegas line of Clemson -3.

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Between Clemson’s obscene pass rush and the Tigers’ desire to protect Bryant from awkward downs and distances, one could see an early lead — for either team — blowing up pretty quickly.

It’s hard to imagine the Tigers finding too much success on the ground, aside from a Bryant keeper or two, but going from Auburn’s defensive backfield to a more mortal one could be like taking the doughnut off a baseball bat. Louisville’s defense isn’t Kent State’s, but it isn’t Auburn’s either, and after brief success last week, the Tigers should find a little more this time around.

And with just a few big pass plays, Clemson could open up a lead and force Jackson to play at a superhuman level, just to keep things within reach.

Of course, Jackson has done that before. The second half in Death Valley, for instance.