Garrett Celek knew things weren't right. He was never meant to be a 311-pound defensive tackle in a 3-4 scheme.
An 11-sack season at Florida State in 2012 led the San Francisco 49ers drafting Carradine with a second-round pick in 2013. The team immediately changed his position, and subsequently, his entire physique. Such a dramatic transition made for four trying years in San Francisco.
Now Carradine feels like he's finally where he's supposed to be. Saleh's 4-3 system has the defensive lineman trimmed down to 273 pounds and back at his natural position. Carradine is currently starting at the "big end" spot, a similar role to what he played in college.
"I'm feeling really comfortable," Carradine said. "I'm glad to be back in a 4-3. This is what I did in college. This is what got me to the NFL. This scheme fits me perfectly."
Saleh has noticed Carradine's upward trend as well and gave the defensive lineman massive praise this week.
"I think he's damn near an elite six-technique," the defensive coordinator said. "To be able to create pocket push from an edge, I think that's where his home is. I think he's pretty freaking good at it. That's where Tank's strength is.
"Will he get some inside rush? Yes. He had some success with it with Denver. But, as a six, dominating tight ends and being able to transition from run thought to pass on first and second down, I don't know if you'll find much better than that in the league."
That is rare acclaim for a player with only one career start. Carradine has 57 total tackles and four sacks in 36 games since 2014. He missed his entire rookie season in 2013 recovering from a knee injury.
Through two preseason games in 2017, Carradine has three tackles and a handful of quarterback pressures. He's shown the ability to push the pocket on base downs before subbing out in nickel situations. His name is still listed atop the 49ers depth chart.
This isn't the first time that Carradine has been the focus of preseason hype. In 2016, he posted 10 tackles and two sacks. Carradine acknowledged Saleh's kind words, and he knows it's time for his exhibition success to carry into the regular season.
"It makes me want to work harder and do everything I can do to help the team win," Carradine said. "I'm going to do everything he wants me to do in order to be productive on the field."
A much-improved Carradine provides yet another piece to San Francisco's deep defensive line. Add Carradine to the list of players who thinks the 49ers defensive front has a chance to be special in 2017.
"This is a really strong group, one of the strongest since I've been here," Carradine said. "We've got guys who can play multiple positions. We've got guys who can do it all."