FORT MYERS, FLA. – Caleb Thielbar developed his best pitch while baseball shut down last summer — and then scrapped it. Which sounds a little weird until you consider the career path that got the lefthander to this point in the first place.

"In some ways," Thielbar joked, "retiring was the best thing to happen to my [baseball] career."

Yeah, this isn't the route most players take, but Thielbar doesn't mind. He is here now, and appears headed to a second career with the Twins that's even more promising than the first.

"I'm just really happy to be back for another year. Honestly, it's all gravy for me now," said the 34-year-old, who after a delayed start due to a sore back will make his 2021 spring debut Monday against Atlanta. "I've got nothing to lose at this point."

That's because Thielbar thought he had lost it all already, during a five-year absence from the major leagues. After spending the 2013 and '14 seasons in the Twins bullpen, the Randolph High School product developed shoulder pain that ended his time with his hometown team. He spent two seasons with the independent St. Paul Saints, and then a couple in the Detroit Tigers farm system, without a call-up.

He took a job as pitching coach at Division II Augustana University in Sioux Falls, S.D. — his wife, Carissa, is an assistant women's basketball coach at South Dakota State — and "I was done with [playing] the game," Thielbar said. "But I guess I wasn't."

Nope, not after the Twins called 15 months ago and invited him back. Not after waiting out the pandemic break and wondering if it would cost him his second chance. And especially not after becoming the Twins' best weapon vs. lefthanded hitters during last year's abbreviated season. Thielbar gave up a measly three singles to lefthanders all year, a .136 average, and was pretty good (.216) against righthanders, too. He earned the Twins' trust, posted a 2.25 ERA in 20 innings, struck out 22 and now is all but assured a spot on the roster next month.

"He's not a young prospect anymore, he's a guy that's just simply on the uptick. He knows what he's doing," Twins manager Rocco Baldelli said. "He was not overwhelmed. He just went out there and pitched. He did such a good job that we kept turning to him. He earned his opportunities. He comes after you with a very unique look."

He almost didn't have it. Thielbar wasn't happy with how he pitched last spring, and when camp shut down due to the pandemic, he was determined to revamp his slider, his putaway pitch against lefthanders.

"I talked about it last spring with the coaches, that I never got a whole lot of swings-and-misses with my slider," he said. "And they basically told me, it's because it just doesn't have any sweep to it. With my arm slot, it's tough to get that."

So he went back to Sioux Falls with a plan, and a stop-motion camera that allowed him to inspect his grip upon release. "I was able to figure some things out, and I actually didn't realize I had," he said. "It's the difference between radar vs. optical [technology]. What I was throwing over the shutdown last year, I thought it was good for a couple of days. To my eyes, it was a good pitch, good horizontal sweep. But it didn't really register on the camera equipment, and then it wasn't quite as good for about two or three weeks. So I kind of scrapped it and went back to what I was doing before."

When summer camp opened and the Twins prepared for a 60-game season, he got into an intrasquad game "and I decided to throw it a couple of times anyway. And [the pitching coaches] came to me after and asked, 'What are you doing? What just happened out there?' " Thielbar recalled. "They showed me the numbers, and they were great. I said, 'Well OK, I guess we'll go with that.' "

Radar technology had picked up the break his slider was producing that the optical cameras hadn't. "It turned out my eyes weren't lying. It really was a good pitch, and I used it all season," he said. "I'm not sure where I'd be if I didn't throw those couple of pitches just for the heck of it."