Todd Grantham had his critics during his time as Georgia's defensive coordinator, and they started growing louder as last season wore on and his defense continued to underperform.

Did Grantham deserve to be on the hot seat after four years of mixed results at an SEC program that demands much more? While outsiders debated his status, Grantham felt perfectly secure with the job he had done, feeling no pressure from coach Mark Richt or anybody else at Georgia.

Yet, eyebrows raised when he decided to leave the Bulldogs in January to become defensive coordinator at Louisville under Bobby Petrino, a man he barely knew. Grantham had two years left on his contract. A month earlier, Richt told reporters he had no plans to change his staff.

So why leave the SEC for a program to enter the much-less-ballyhooed ACC?

Grantham gives many reasons for his decision, one that looks better and better as the season has worn on. In place of constant criticism, Grantham has garnered high praise for the job he has done with the Louisville defense. Somewhat surprisingly, his defense has been the story of the season for the Cards -- and the biggest reason for hope against No. 2 Florida State on Thursday night.

“I don’t think I needed a fresh start. I just think you always look for challenges,” Grantham said in a recent phone interview. “I had a great time at the University of Georgia. We did a lot of great things there. We got the program back to where it needed to be. By being able to come here with Bobby, able to hire my brother [Tony], able to be a part of something different, I felt it was a good opportunity.”

Not many expected this type of performance from the Louisville defense, despite its overall strength under former head coach Charlie Strong. Louisville had to replace seven starters off the No. 1 defense in the country in 2013, including two first-round picks.

Plus, the Cards had to learn a new defensive scheme, one that shifted players away from the 4-3 and into the 3-4. It is a style that first caught Petrino’s eye back in 2010, when his Arkansas team had to face Georgia in Week 3. Grantham was in his first year with the Bulldogs, coming over from the Dallas Cowboys.

Petrino said his staff studied Dallas the entire offseason to get a good grasp of what Grantham would do.

“We had two games early in the year that we should win,” Petrino said. “So we took a long time to get ready for that game and watched what he did the remainder of that year and the next year. I thought he did an excellent job.”

Arkansas ultimately won the game 31-24, but Petrino never forgot the fits Grantham gave his offense. That’s why Grantham was at the top of his list when he arrived back at Louisville. Petrino never had a team use a base 3-4 before, but he was willing to make that change to get Grantham on board.

Players slowly adjusted in the spring. Many were shifted around to different positions to better fit their strengths.

But there were hints this defense would be just fine. Several talented players returned, including Lorenzo Mauldin, James Burgess, Keith Kelsey and Gerod Holliman. The defensive group heard all the doubters and used that as motivation. There was no way they would take a step back.

So Grantham got himself a group of players not only motivated, but dedicated to mastering the new defensive scheme. Players held film study sessions on their own. Those who were told to get bigger did. Those who were told to lose weight did.

“This offseason, I’ve never seen a group of guys work so hard,” said Burgess, who added 10 pounds. “Everyone wanted to buy into the coaching schemes, understand what they were being taught and apply it to the field.”

When August rolled around, Grantham realized he might have a pretty stellar group on his hands.

Louisville remains the No. 1 total defense in the nation in 2014 and is actually giving up fewer total yards per game and fewer rushing yards per game than a year ago while playing a more difficult ACC schedule.

The Cards also are averaging more sacks per game than last season and more turnovers per game as well. Impressive improvements considering all the new starters, all the position changes and the scheme change.

“You never know what we’re going to hit you with,” Burgess said. “We have so many disguises, so many different play calls ... we have one of the most difficult playbooks, and that’s what makes us so great on defense because we all understand what we’re being taught every other week and why we’re doing it.”

Players also have embraced Grantham and his “rowdy” personality. “I love playing for him. I wish I could play for him for five more years,” Burgess said.

So it turns out, Grantham knows how to coach -- though he is above screaming, "Told you so!"

“As a coach, you always have pride in your work,” Grantham said. “The thing I always want our players to do, I want them to play hard, I want them to play fast, and play aggressive. We’ve been able to get our guys to play to their ability and play with that identity we talked about. That’s the beauty of coaching. That’s the fun part.”

More fun may be in store, depending on what happens Thursday.