PORTLAND, Maine -- On May 7, 2023, Marcelo Mayer was wrapping up a career day for High-A Greenville. He opened the Sunday matinee 3-for-3 with a homer and a double and connected on another extra-base hit in the eighth inning, when he tripped on the basepaths and landed sharply on his left shoulder while trying to leg out a triple that would have given him the cycle. It is still one of the shortstop’s two four-hit performances in the Minors; the other came four days earlier.

The Red Sox's top prospect (MLB No. 11) remained in the game but didn’t return to the Drive lineup for another week. The May 14 results at home couldn’t have been more different -- 0-for-4, four strikeouts. Mayer may have been back in the lineup, but he hit just .190/.256/.366 with a 25.5 percent K rate over his final 55 games for Greenville and Double-A Portland until being shut down in early August.

The left shoulder impingement did more than just zap Mayer of his power and impact at the plate; it altered the mechanics that made him a promising hitter in the first place.

“It affected pretty much throughout the whole swing,” said the 2021 fourth overall pick. “I had to change my stance. I had to change where my hands went. And then throughout the swing, it still didn’t feel natural … I widened out to try to put bat on ball and simplify things. But I wasn’t me for sure.”

After spending much of the offseason pinging between Boston’s complex in Fort Myers, Fla. and his home in California -- with stops in Massachusetts for rookie development camp and Red Sox Winter Weekend -- Mayer got back to swinging around late January, and he’s taken off ever since without needing to account for the left shoulder.

Entering Wednesday, he leads Double-A with 21 doubles. He also ranks among the level’s top half-dozen in runs scored (45, second), extra-base hits (27, third), hits (63, third) and total bases (102, sixth). The left-handed slugger sports a .300/.370/.486 overall line over 238 plate appearances.

By no longer having to stand out wide, Mayer has found himself letting his gifts play more naturally and comfortably. But that’s only part of the equation. He’s also only a 21-year-old who is still maturing physically.

“I definitely have gotten stronger, gotten quicker,” he said, “so I think all of that plays a factor too.”

That combination of strength, agility and health may be most notable in Mayer’s ability to turn around fastballs in 2024. Last year with Portland, the infielder hit just .146/.253/.268 against heaters and missed on 19.9 percent of his swings, per Synergy Sports. This season, that slash line is up to .393/.447/.598, and the whiff rate has dropped to 10.5 percent.

Mayer is at his best when he’s lacing liners to the pullside, and his ability to connect on velocity has helped his line-drive rate jump from 15.3 percent in the Eastern League last year to 28.4 percent through the 2024 season’s first two months.

But ask the player, and he’s just as proud about the pitches he’s laying off more now than the ones he’s crushing.

“Definitely the backfoot slider,” Mayer said. “I think that one got me a lot coming into Double-A. I got exposed a little bit. With the shoulder injury too, I feel I had to do too much with hands because I didn’t feel quick enough. Then obviously the fastball up too, I think those two pitches together. When I lay off them, they have to come in the zone, and that’s when I’m able to do damage.”

True to that statement, Mayer has swung at only two of the 30 sliders he’s seen down and in for a swing rate of 6.7 percent. In 2023, that was up to 37.5 percent (nine of 24).

These are notable, trackable changes that have solidified the Golden State native’s place among the game’s best prospects when healthy. But by his own admission, these positive developments don’t make Mayer a finished product, far from it. He talks to his father Enrique twice daily -- once in the morning, once at night -- to chat life and analyze each of his Sea Dogs at-bats. (Dad watches from home on MiLB.TV.)

That paternal hitting instruction led to one change that has helped the prospect unlock another gear through May and June.

“I’d say a big one was toning down my leg kick a little bit,” he said. “I made it a little bit more of a stride just because I felt a little bit inconsistent at the beginning of the year. I was still having results, but I still didn’t really feel like myself. I toned it down, and ever since then, I’ve been hitting the ball pretty hard.”

Sixteen of Mayer’s 31 hits in May went for extra bases, and this month -- despite his place in a loaded Portland lineup alongside Top 100 prospects Roman Anthony and Kyle Teel -- Eastern League pitchers are working around him with 10 walks and only three strikeouts through his first eight games.

More alterations and tweaks are still likely ahead for Mayer, perhaps starting with improving his splits against fellow lefties (.192/.264/.298 through 53 plate appearances). But there’s a certain temptation to believe he isn’t far from joining Triple-A Worcester for the first time. The Red Sox even mixed in a second career start at third base on June 5 -- the first came last year when Trevor Story rehabbed with Portland -- to potentially increase Mayer’s versatility in a move many organizations make when the Majors are in sight.

Then again, this is a Red Sox MLB club whose shortstops rank 24th in The Show with a collective 0.5 fWAR. Story is expected to be out until 2025 following shoulder surgery, and while David Hamilton has shown flashes this spring, Mayer is widely thought to be the better long-term option at the six. Considering he’s only two stops away, there could be a path to Fenway Park for Mayer as early as this summer or fall.

Just don’t expect Mayer to get too comfortable along that journey, even as his shoulder holds up and the results roll in.

“Sometimes, I’m going to have to change my leg kick,” he said. “Sometimes, I’m going to have to change up my hands. A big part of the game is being able to adjust.”