Red Sox’ Isiah Kiner-Falefa started swinging as hard as possible. It almost broke his arm.

When the Red Sox were playing poorly, and he was barely playing at all, Isiah Kiner-Falefa thought his career was close to over. With nothing to lose, he adopted a new offensive approach in May: Swing as hard as possible every time.

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By the end of the month, his left forearm started to hurt. Now, he is out indefinitely because of a stress reaction — a precursor to a stress fracture — in his ulna, a bone in the arm/wrist.

Kiner-Falefa attributes the injury to the all-out swings as well as the extreme volume, up to 300 swings per day when he wasn’t in the lineup, he said.

“I was working at a crazy, crazy rate that I’ve never worked at before,” he said. “I would go to [batting practice] and swing as hard as I could, just to try to get myself in the lineup. And it worked. Then I paid the price.

“I don’t regret it one bit. So it’s kind of on me, but it’s not on the organization, nothing to do with them. It’s just the workload that I put in. I don’t regret it, because I got myself in a spot that I haven’t been in.”

Kiner-Falefa’s wicked swings came with tangible proof.

His bat moved at an average of 66.6 miles per hour in 2025.

By the end of April, it was 67.7. In May, 68.6. In his partial June, as his forearm worsened, 69.5.

Those are significant increases, especially for a light-hitting veteran infielder. The underlying idea: The faster a batter swings, the harder he hits the ball, the more likely he is to do damage.

Over the month before being sidelined, Kiner-Falefa slashed .312/.384/.429, good enough to become an everyday player again. His last at-bat was a home run.

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“I was having so much success, it was like, dude, I don’t want to come out. I’ve never felt this good in my whole career,” he said. “[Eventually the arm] was throbbing at night. I’d go to sleep and it’d wake me up all night, just pounding. It was like I had a headache in my arm almost.”

Fortunately, he added, the Red Sox “caught it before [the bone] could break-break.”

Kiner-Falefa feels as though he has unlocked a new version of himself. Previously, he “tried to play defense in the box,” he said. This is a more proactive approach. After lifting heavy and getting stronger during this downtime, he plans to keep up the as-hard-as-possible swings upon returning.

“My body wasn’t used to me swinging hard,” he said. “It’s a price I gotta pay, but at the same time, it made strides in my career that I haven’t made before. So it sucks. But I know what I have to do to get it back, so now we just have to wait to get healthy.”

Marcelo Mayer suffered the same overuse injury (though less severe) to the same bone at about the same time. He went on the injured list Friday after fighting periodic pain for a couple of months.

“Weird. Weird. Very weird,” Kiner-Falefa said. “We’ll see if it pops up again with someone else.”

It is “possible” the Red Sox activate infielder Romy Gonzalez from the injured list on Sunday, Tracy said . . . Cohasset native Ben Rice in 15 games at Fenway for the Yankees: 8 for 50 (.160) with 12 strikeouts and no home runs . . . The Red Sox announced a sellout crowd of 36,026 . . . Lefthander Jovani Morán (left elbow inflammation) will make one more rehab appearance, throwing an inning-plus with Triple-A Worcester on Sunday, per Tracy . . . Brockton native AJ Dybantsa, selected first overall by Washington in the NBA Draft, threw out the ceremonial first pitch, lobbing a strike to Payton Tolle . . . Katie Reynolds (Watertown) and Beth Greenwood (Amherst, N.H.) of the Boston-named squad in the nascent Women’s Professional Baseball League also threw out first pitches . . . The Red Sox are collecting monetary donations to be directed toward disaster relief efforts in Venezuela. Visit RedSoxFoundation.com/Relief for more information.

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