On one side of the New York Yankees clubhouse, Aaron Judge’s locker stands near the door to the training room, where the reigning AL MVP is receiving treatment for a toe injury that has kept him out since June 3. All the way across the room, next to the door that leads to the batting cages, lockers for three outfielders stepping up to take critical at-bats in New York’s hobbled lineup occupy another corner. The outfielders themselves are usually down the hall, taking swings.

Jake Bauers, Billy McKinney and Willie Calhoun — all 27 or 28 years old, all acquired within the past 13 months for cash or in minor-league free agency — were pegged for a combined total of 148 plate appearances this season (all by Calhoun) in preseason projections at Baseball Prospectus. As we approach the All-Star break, they have already taken 370. Working to help the Yankees bridge a variety of injuries that now includes the mammoth gap left by Judge — who in 2022 delivered a mind-boggling 62 homers and 11.5 Wins Above Replacement — these three are flesh-and-bone versions of what the R in WAR conceptualizes.

They are replacement players.

“There's going to be five guys no one even had projections for that are now going to be playing integral roles,” Yankees hitting coach Dillon Lawson said. “And how they do in that time is huge.”

The outfielders testing their mettle in the Bronx are doing so under a particularly bright spotlight, but they are part of a huge, varied group of players constantly scrutinized and prized for their potential to provide a season-shifting edge — professional ballplayers still looking for a permanent foothold in the big leagues, but with enough proven skill to become the answers every MLB team will seek when, across 162 games, their plans are inevitably forced to change.

Getting the most out of these readily available players is extremely valuable. Executives across MLB, however, agree that there aren’t obvious methods to locate the best of the talent floating on the fringes of major-league rosters.

“It’s very, very difficult to predict which players that have had Triple-A success and then have been unsuccessful in limited major-league opportunities are going to be successful,” Baltimore Orioles GM Mike Elias told Yahoo Sports earlier this season.

Even as deeper, more workable data continues to proliferate in the sport and roster churn ramps up every year, evaluating these players is a code that remains largely uncracked.

“I think if ever there was an area in baseball right now to carve out an advantage,” Elias said, “it would be in becoming incredibly smart with that population of players.”

Replacement player? Quad-A player? Or becoming something more?

In conceiving of WAR, the now-ubiquitous value metric that quantifies players’ overall contributions to winning in baseball, the statistical pioneer Tom Tango needed a specific baseline. He defined it as “the talent level for which you would pay the minimum salary on the open market, or for which you can obtain at minimal cost in a trade.”

We’re talking waiver claims, minor-league free agents, players traded for cash or 28-year-old relief pitchers in Double-A.

For the purposes of creating the statistic, FanGraphs and Baseball-Reference don’t adjust WAR based on live tracking of this class of player. Instead, the hypothetical production of a replacement player is estimated and crunched into a static level based on how a full team of them would likely perform across a full season. When you see Judge’s 11.5 WAR from 2022, it reflects the cumulative total of wins his play was likely to create above that hypothetical replacement-player level, taking into account factors ranging from his historic home run total to his capabilities in center field.

The actual players on the waiver wire or catching an emergency flight from Triple-A to the majors are not hypothetical. And major-league clubhouses certainly do not view their impromptu teammates as “replacement players” or “Quad-A players,” the colloquial designation for those who have gotten results in the minors but not at the major-league level.

Instead, teams view these additions as players somewhere in the life cycle of becoming an established major-leaguer. A veteran waiting to happen.

“When I think about that, it's like guys who have been up and down, who have 14 cups of coffee, you know, but have never gotten, like, a full shot,” said Collin McHugh, the Atlanta Braves pitcher in his 11th big-league season. “Every year, you see some of those guys actually get an extended chance and prove themselves and really get some momentum with a career and can move forward.

“I was kind of that guy.”

McHugh, now 36, has pitched in five postseasons and won a World Series ring with the 2017 Houston Astros. When he joined Houston, though, he was a 26-year-old waiver claim with an 8.94 ERA in 47 1/3 MLB innings spread across two intermittent seasons and two franchises.

“They were like, ‘Well, you're too good to pitch in Triple-A, but your numbers in the big leagues stink,’” McHugh said, recalling the no-man’s-land he occupied with the New York Mets and Colorado Rockies.

At the time, the Astros were in the depths of their rebuild. They snagged a bevy of players they found interesting and threw them into consistent action at the highest level. McHugh, eventual Cy Young winner Dallas Keuchel and others turned into members of the team’s core.

Similar stories pop up on almost any team not fully loaded for contention — because players often capitalize on playing time. Brent Rooker has 14 homers and a 128 OPS+ for the Oakland A’s after joining on a waiver claim. Mike Tauchman has won a job leading off for the Chicago Cubs.

Elias, then the Astros’ assistant GM, readily recalled that lesson when he began a new rebuild in Baltimore. The Orioles, now flying out of their rebuild with baseball’s third-best record, regularly rely upon contributors claimed off waivers (Jorge Mateo, Ramon Urias, Bryan Baker, Cionel Perez), plucked in the Rule 5 draft (Tyler Wells, Anthony Santander) or acquired for nothing more than cash considerations (Ryan O’Hearn) to supplement the team’s top draft picks and acclaimed prospects.

“I think one of the more under-noted aspects of rebuilding,” Elias said, “is you have all this playing time for young, interesting players that have been squeezed out of other rosters.”

How eventual stars wind up on the move

All baseball teams — even the best and most win-now-focused among them — are limited by 26-man active rosters and 40-man rules designed in part to keep big-league-caliber players from stagnating interminably in one organization. So even with fewer spots dedicated to the process, competing teams are often busy sifting for gems.

“We're constantly keeping abreast of who's available, and every day when the waiver wire goes out, we're drilling down on who could potentially be fits,” Philadelphia Phillies GM Sam Fuld said. “We're always looking to upgrade our team from top to bottom.”

If anything, teams gung-ho about the postseason might be more liable to run into the unexpected obstacles of injury or poor performance. Chris Young, GM of the first-place Texas Rangers, would likely be in a much different situation right now without the emergence of role players beyond the big-ticket free agents at the top of his team’s roster.

“Something I’ve learned in the general manager chair is the value of a functional 40-man,” Young told Yahoo Sports. “We’ve not had that my first two years. And then now this year, I feel like we have a much more functional 40-man roster, and it's given us depth and quality replacement-level players when we’ve had injuries or guys underperform.”

Both during rebuilds and in the shift toward all-out pennant races, the process forces decisions before all the relevant information can be known. Consider a selection of key players on contending squads:

• Adolis Garcia, the Rangers outfielder who ranks as one of the 20 best players in baseball this season by FanGraphs WAR, became available in 2019 because the St. Louis Cardinals cut him after just 17 major-league plate appearances to make room for pitcher Kwang-Hyun Kim.

• San Francisco Giants second baseman Thairo Estrada, about as productive as Mookie Betts or Mike Trout this year, was designated for assignment by the Yankees to squeeze the more proven Rougned Odor onto the roster of a contending team.

• Evan Phillips, the Los Angeles Dodgers’ best relief pitcher, cycled through a procession of the game’s sharpest organizations — Braves, Orioles, Rays — before finding himself with the Dodgers on a waiver claim.

And the churn never, ever ends.

In a sport that inherently spreads responsibility thin by mandating a batting order and restricting substitutions, the extreme demands of playing in the contemporary game force teams to distribute those responsibilities even further. The 2023 Yankees, for instance, have used 21 hitters and 22 pitchers already this season, whereas the 2009 Yankees used 22 hitters and 24 pitchers all year.

What’s more, injuries to starters and star players can’t even be called unexpected at this point.

“I think we all understand the importance of depth and finding players that bring value that might not cost a lot. With the amount of injuries that exist in the game, I think it's another reason why that sort of decision-making is so important,” Fuld said. “You just have to dip into your depth way more than, you know, say, 20, 30 years ago, when injuries were less frequent.”

The stakes of this game within the game appear to be rising. Nowadays, more players are required to field any team. More better players are required to field a good team. In a multibillion-dollar industry, there is incentive to keep trying to find someone better.

“It really is, like, an opportunity,” McHugh said, “mixed with a little bit of fortune.”

Is that minor-leaguer good? Or just feasting on 92 mph fastballs?

The front offices on the other side of the equation, it turns out, feel much the same way. One significant issue in spotting future major-leaguers is the chasm between major- and minor-league pitching, according to Tampa Bay Rays hitting coach Chad Mottola.

“That gap has widened,” Mottola said, “and there’s nothing you can really do as a player because you’re having success, and you think you’re doing the right things.”

Having helped a cadre of young or unproven players including Josh Lowe, Luke Raley, Taylor Walls and Isaac Paredes make vast improvements at the plate from 2022 to 2023, Mottola pointed to focused offseason changes tailored to top-tier competition, unfettered by the confusion of the minors.

“You kind of have to see it to believe it,” Mottola said of major-league pitching. “Whether it’s an offseason or getting sent back to the minor leagues, that’s what’s happening so much more. It’s almost become the normal — it’s, ‘OK, I got to see it. Now let me go make adjustments.’”

Browsing leaderboards of the best statistical hitters from the upper minors in recent seasons can feel more like roulette than logic. A lot of that has to do with the unabated spike in the quality of pitches and pitchers at the highest level of baseball.

“We're well aware that the seventh and eighth guy out of a major-league bullpen is a lot different than what guys are seeing at the Double-A, Triple-A level,” said Fuld, the former Rays outfielder turned Phillies GM.

On the flip side, what helps front offices and coaches understand a player’s potential is having him in the building. Fuld said front offices don’t have “the magic recipe” for identifying useful pieces on the wire, so they prioritize underlying traits that “might not bubble to the surface on a triple-slash line.”

Those traits, Fuld said, include physical ones — the power potential, speed and hand-eye coordination measured in increasingly granular detail across organized baseball — as well as the emotional and mental qualities that give some players a leg up in quickly picking up new concepts.

“You're limited to what you can actually detect from the outside looking in,” Fuld said. “You do your best to get as much information on a player as you can leading up to the acquisition, but you learn a whole heck of a lot more once you get your hands on him, get to know him on the human level, once our staff gets to spend hours with him in the cage.”

All of that begins to melt into the art of player development. The Los Angeles Dodgers have made a habit of transforming readily available minor-league free agents (see: Max Muncy) and waiver claims into stars with a combination of targeted acquisition and tailored instruction, and now every team — with varying levels of success — is working to replicate that extreme-makeover model.

The Phillies, for example, have the spark of something working with Cristian Pache, the slick center fielder and former top prospect whose bat never took off with the Braves or A’s.

“They're not necessarily the headline-grabbers,” Fuld said of such players. “But as we know, the back end of the roster and the depth that we have in the organization is how you have success and have long-term, sustainable success.”

What’s on the line for the contributors you didn’t see coming?

Jake Bauers does not sit around thinking about his role filling in for Aaron Judge, nor does he linger on the stakes of his performance.

A left-handed outfielder and first baseman, he presented the selective approach and impressive exit velocities of a power hitter in stints with Cleveland, Tampa Bay and Seattle, but he never found the actual power in games. He entered 2023 with a career .348 slugging percentage in the majors and a 78 OPS+. With the Yankees, however, he has already belted seven homers — buoying a .470 slugging percentage — after crushing nine in 21 games at Triple-A this season. What he’s thinking about now is the improved routine he developed in Scranton. He’s thinking about maintaining the work he has done with Yankees coaches to keep his bat path flatter, allowing him to take more advantage of his latent power.

“I look at it like showing up to the yard, getting ready to play a baseball game, right? I think once you start thinking about all that extra stuff is when things can kind of get a little bit complicated in your head and kind of mess with your approach on the field,” he said. “So really just been coming in, day by day, trying to help this team win games.”

Since May 29, when Yankees center fielder Harrison Bader began a brief stint on the injured list — Aaron Judge would follow a few days later — Bauers (.875 OPS) and Billy McKinney (.807 OPS) have been two of the team’s three best hitters.

They have also been the Yankees’ only hitters with above-average batting lines. That is not a recipe for success, no matter how good the replacement players are, but it does demonstrate the ways in which a baseball roster in 2023 is many versions of a team packed into one frame — and how every version needs capable heroes.

The Yankees have squeaked out a 16-16 record in the hobbled month or so since Bader went down, which could be much worse. Meanwhile, the Orioles have a 15-15 record since they picked up Bronx castoff Aaron Hicks for the league minimum to cover for then-injured center fielder Cedric Mullins. This season, a playoff spot or playoff seeding could easily hinge on these small differences in the AL East.

Many under-the-radar additions might be counted on come September, too. The expanded MLB postseason that took effect in 2022 makes it tougher to identify clear trade deadline sellers. Four AL teams and seven NL teams are more than five games out of a playoff spot as of Thursday, with two of those being the painfully disappointing New York Mets and San Diego Padres.

Point being, there are probably more teams that would like to employ Bauers or McKinney or the currently injured Calhoun than there are teams aiming to dangle a clear upgrade in front of the Yankees.

And so for as long as Judge remains sidelined, at least one of the trio is likely to get a chance to play, to wipe away any recollection of how they became 2023 Yankees and instead leave a mark on the season’s outcome.

“You never know whose two weeks turns into 12 years,” Lawson, the Yankees hitting coach, said. “It all has to start somewhere.”

Hannah Keyser contributed reporting to this story.