Louisville's experiment with true freshman quarterback Lamar Jackson in 2015 amounted to this: Go make a play, Lamar. Coach Bobby Petrino put it nicely when he said, "There would be times when you'd say, 'He had no idea that play, did he?'"

Nope, he didn't. Ever.

"I really didn't know any of the plays last year," Jackson said. "Coach put me out there and gave me certain (plays) that he did think I knew. He'd put me out there and I'd just stare down receivers. If it wasn't open, I'd just run."

So Jackson ran and ran and ran to the tune of 960 yards, including a school single-game quarterback rushing record of 184. In the process, he helped the Cardinals finish 2015 with six wins in its final seven games. Jackson's development as a passer and the return of 17 starters has Louisville thinking big in 2016.

This is Year 3 of Petrino's return to Louisville, and it comes after 9-4 and 8-5 seasons. By the end of his third year at Arkansas and during his first stint at Louisville, Petrino had produced a 10-win season. That's very possible in 2016. While Clemson and Florida State control the ACC and dominate the headlines, Louisville is quietly lurking as a major threat.

"They had some dudes (in 2015) and I think they're going to continue to play at a high level," Clemson coach Dabo Swinney said. "Nobody will be excited to play Louisville, I promise you."

Louisville, ranked No. 20 in the CBS Sports 128 preseason rankings, lost 20-17 to Clemson last season after an incomplete pass from the Tigers' 2-yard line with 21 seconds left. The Cardinals lost 41-21 to Florida State in 2015, but Louisville led 7-6 at halftime before losing control in the second half.

Petrino said "we're there" with depth to compete against Clemson and Florida State. "We feel like we're a very talented team. We've got the type of speed you need to win in this conference. We've got playmakers on both sides of the ball and we know we've been close."

Louisville returns linebackers Devonte Fields and Keith Kelsey, nose tackle DeAngelo Brown, and safety Josh Harvey-Clemons. All of them entertained leaving early for the NFL. "That was one of our biggest recruiting jobs, there's no question about that," Petrino said.

Louisville has become a home of second chances. Petrino compiled a roster featuring several key transfers:

Fields, a former Big 12 Defensive Player of the Year at TCU, led the country last season in tackles for loss per game (1.73). He was kicked out of TCU in 2014 after an arrest for misdemeanor assault against an ex-girlfriend. Fields agreed to have the charge dropped in 2015 in exchange for completing four anger management courses.

Harvey-Clemons was an All-ACC honorable mention safety in 2015 with 88 tackles after starting 11 games at Georgia as a sophomore. He was dismissed by Georgia after violating the school's drug-testing policy for the second time.

Shaq Wiggins was an honorable mention All-ACC starting cornerback last year who lead the team with 11 pass breakups. He transferred in from Georgia in 2014 and said he was looking for a program that would "embrace my personality, someone who is a jovial, carefree and a bit of a jokester, but who knows when to put jokes aside, get focused and become a true competitor, especially when on the field." Petrino threw Wiggins out of a practice in spring 2015.

Ja'Quay Savage is projected to be a starting wide receiver after making six starts in 2015. He transferred in 2014 from Texas A&M, where he was known as Ja'Quay Williams.

The Cardinals' recruiting classes since Petrino returned have been ranked as fairly average in the 247Sports Composite: 38th in 2016, 32nd in 2015 and 45th in 2014. More than many coaches, Petrino banks on transfers and he signed 16 junior college players in his first three years back.

The depth on the roster is where Petrino wants it. In Petrino's first year, Louisville lost 23 seniors and four juniors from the previous team.

"It was like you lost a whole roster so we had to play guys young last year," he said. "But we won't be like that this year."

Louisville decided the quickest way to play Jackson as a true freshman quarterback was predominantly in the shotgun. That's rare for Petrino, who prefers quarterbacks to be under center.

During bowl practices and in the offseason, Jackson began learning to take snaps from under center. Petrino said Jackson hasn't had issues with taking snaps, and now it's about getting his footwork correct to help the run game and play-action passes.

"The good thing now is he really understands the concepts," Petrino said. "He can sit down and you give him a play and he can draw up every route and where everybody is at, and he knows his progressions versus this coverage or versus that coverage."

Over the final five games of 2015, Louisville averaged 35.6 points compared to 24.4 points for the first eight games. Granted, the five-game finish was against Syracuse, Virginia, Pittsburgh, Kentucky and Texas A&M -- that's not exactly scoring on Clemson and Florida State -- but when Petrino's teams are clicking, they score a bunch of points.

"Our offense needs to get to the point that every time we take the field we expect to score, because that's the tradition of Louisville offenses," Petrino said.

We will know very early in 2016 if Louisville is for real. The Cardinals host Florida State on Sept. 17 and travel to Clemson on Oct. 1. Louisville is conditioning harder earlier in camp than usual because it's playing both ACC Atlantic Division contenders so soon, something Petrino doesn't sound like he's happy about.

"Nobody would listen if you complained so don't complain about it," Petrino said. "You might not understand it or what people are thinking, but it is what it is."

Quietly, Louisville is staking out its position to ruin the narrative that the ACC is only about Clemson and Florida State. If Jackson plays all year like he did late in 2015, the ACC script may need to get rewritten.