GREEN BAY, Wis. -- It must have been an odd sight if any of his neighbors in Green Bay got a glimpse of what was happening in JC Tretter's garage this spring.

There was the 6-foot-4, 307-pound Packers offensive lineman bent over in a three-point stance snapping a football – to his sister.

But in many ways, it made sense that Tretter would be snapping a ball to whomever, whenever and wherever he could. After all, he was being touted as the leading candidate to become the starter at a position he has never before played.

"It was tough because it's tough to get a ball in your hand with all the rules in the CBA," Tretter said. "Whenever you can get the opportunity, you've got to take advantage of it. You've got to go find a park somewhere or something, and that's frustrating."

A college tackle at Cornell, the fourth-round draft pick in 2013 did not even begin practicing at center until Nov. 19 of last year, when he took part in his first-ever NFL regular-season practice. And now, here he was as the leading candidate to replace Evan Dietrich-Smith, the Packers' starting center from last season who left in free agency to sign with the Tampa Bay Buccaneers.

Tretter broke his ankle last May on the first day of his first OTA practice as a pro. He missed the rest of the offseason program, all of training camp and began the season on the physically unable to perform list. It was not until late November that he was even allowed to practice. Although he never was active for a game, it was during those late fall practice sessions that the idea of him transitioning to center was born.

That led to an offseason in which Tretter was determined to spend as much time as possible – and as much time as the collective bargaining agreement allowed – at Lambeau Field.

"When I was leaving the facility after our loss in the playoffs, it was, 'I'm going to come back and train like I'm going to be the starter,'" Tretter said. "No matter who they bring in or who they bring back, my goal was to come back ready to be a starting center in this league."

The Packers feel like he has done that. Even after drafting a potential starting center, Ohio State's Corey Linsley in the fifth round, the Packers opened OTAs last week with Tretter in front of quarterback Aaron Rodgers.

"JC's doing a really good job," Packers coach Mike McCarty said. "I think he's been here every single day since the season ended. I don't think there's been a day that I've walked through the locker room from February all the way through that he hasn't been here. I think that is really shown as far as the way he's jumped in there. So far, so good. I've been impressed with what I've seen."

Because the rules of the CBA prevent players from working directly with coaches – or even having a football in their hands at the team facility – before May, Tretter had to get creative. While he spent hours with the team's strength/conditioning and nutrition staff, he had to go elsewhere to get in his snapping work. Shortly after the season, he went back East to work out with former Cornell quarterback Jeff Mathews, who was training for the combine and would eventually sign with the Atlanta Falcons.

"So I got to snap with him, and that was the main goal of going to New Jersey to train with him, was to get a quarterback there to work with," Tretter said. "Then I came out here a couple of months before everybody else came back."

Said offensive line coach James Campen: "The thing with him is he's very smart. He's got good leadership ability, a hustler, works extremely hard. He's got very good balance and he's a big, strong guy. He's a bigger man and his work ethic is outstanding."

The final point, Campen's praise of Tretter's work ethic, takes us back to Tretter's garage, where he was firing shotgun snaps to his sister, Katherine.

"She's good; she has a great cadence," Tretter said. "She was giving me protection adjustments. She was on top of her stuff."