MESA, Ariz. — The Cubs were the first team to contact right-hander Brad Keller when free agency opened this winter, a gesture he appreciated. And when it became clear they would be able to sign him to a minor-league deal with a spring-training invite, they jumped.

“There were some changes we started to see at the end of last year that gave us some pretty good confidence that we were going to see a little bit of a velo trend,” Cubs pitching coach Tommy Hottovy said in a conversation with the Sun-Times. “Maybe not to 98.”

And yet, that’s about what Keller has thrown this spring. In the Cubs’ Cactus League opener, he touched 97.9 mph, and his fastball averaged 96.3 — about three mph harder than the last two seasons. That caught the attention of his new teammates, and even the members of the coaching staff who already had some idea of his progress.

“Brad Keller certainly was a little more than we expected,” manager Craig Counsell said the next day. “And that’s always a good thing.”

With roster decisions fast approaching, the Cubs now have to decide whether they want to continue to stretch out Keller. And that will hint toward whether they view him as a starter or multi-inning leverage reliever.

The changes that had intrigued the Cubs in the first place started with a midseason switch in teams for Keller. After being designated for assignment by the White Sox in late May of last year, Keller signed with the Red Sox.

“They gave me three or four drills,” he said. “Because I kind of have a long arm action, so they wanted to tighten that up. And then they noticed that I will, at times, get a little spinny in my delivery.”

Of those drills, Keller saw feedback from the “Kikuchi drill” right away. He had heard of it before from working with the Maven Baseball Lab in Atlanta.

In the drill, Keller pushes up onto the tiptoes of his back foot and then drops down before pushing off. It forces him to use his back leg to generate power and keeps him moving in a straight line down the mound.

“I’ve always heard it my whole career,” Keller said of using his legs more, “but actually being able to have tangible drills that I can repeat helped me a lot.”

He draws a direct line between his old delivery — “basically throwing with all arm” — and the thoracic outlet syndrome he battled in 2023. He underwent an operation to address the issue that offseason.

“Basically I was just reaching back, and the further I reached away, I was pulling my neck and all that fun stuff,” he said. “It was terrible.”

Keller attributes part of his velocity jump to his health. The mechanical adjustments and drills associated with them — as Keller “ran with” the feedback from the Red Sox and then returned to Maven in the offseason — took care of the rest, while also serving as an injury-prevention tool.

Over the course of Keller’s career, his season velocity peaked in 2022, when his fastball averaged 94.5 mph.

“I’ve always shown flashes of throwing hard but never consistently,” he said. “Maybe one pitch, two pitches here and there throughout a game.”

By the end of last season, Keller’s velocity was trending up. In his last outing, a four-inning relief effort, his fastball was sitting at 95 mph.

Said Hottovy: “Our pitch this off season to him, when we were talking to him, was, ‘Look, here are some things that we were seeing and were trending. We want you to continue on that,’ hoping that we would see velocity increase from that point. Which we have.”

To kick off Cactus League play, Keller threw scoreless outings against the Dodgers (1⅔ innings) and Padres (two innings).

In his last appearance, against the Guardians last Saturday, Keller allowed four runs in 2⅓ innings. Hottovy saw a pitcher who threw well in his first inning, faced five straight left-handed batters and worked through things his next, and fatigued the third time out. The main goal was upping Keller’s workload, which they achieved.

“In terms of how his stuff looked, velocity is in a great place, pitch shape is in a great place, mechanically he feels good, he’s recovering well,” Hottovy said. “He’s checking all these boxes.”