It's September, which means fall is in the air and postseason baseball is right around the corner. The MLB's final 12-team field is not quite set, but we generally know the pretenders and contenders. Teams in that latter category are doing everything they can to one-up the competition and find a new edge amid September roster call-ups.
That generally means bringing top prospects in to the big leagues, often for the first time, just to see if they can hack it before the postseason. Odds are a lot of September call-ups get phased out of the regular lineup or rotation come October, but every season there are a couple that break through.
As for the burgeoning stars with the most to prove in this final month of the regular season, many of them are, in fact, future lynchpins on a contender. But sometimes there are less established teams in the middle of a youth movement, hoping to find that spark of optimism for next season and beyond.
Here are five rookies (or sub-rookies) facing the greatest pressure as the 2025 campaign winds down.
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5. C/OF Harry Ford, Seattle Mariners
As rosters expand, the Seattle Mariners will welcome their No. 2 prospect Harry Ford into the fold. Ranked No. 39 overall at MLB Pipeline, Ford's call-up was a long time coming. He's only 22, but he has been rock-solid all season in Triple-A, giving the Mariners every incentive to promote him and see what happens.
Here's the situation: Seattle is in a bit of a collective rut. That means Ford can meaningfully change the chemistry of this team and even earn starting reps for October if he performs well. The door is wide open. Well, almost. Ford is a catcher by trade. That happens to be the position occupied by MLB home run leader and AL MVP frontrunner Cal Raleigh. Those reps will be few and for between for Ford.
Instead, the Atlanta-born backstop will need to learn a new position: outfield. Seattle's outfield depth chart has a few holes he can capitalize on. Ford has a .283 average and .868 OPS through 97 games in the Minors this season, belting 18 homers and driving in 74 runs. He's a stellar athlete, more than capable of covering the necessary ground in left or right field, and the bat projects well. But it's hard to adjust to a new level of competition while also playing a position he is less familar with.
Seattle can get creative, perhaps engineering DH reps for both Ford and Raleigh, but in order to maximize his short- and long-term value with this team, the Mariners will want Ford in the field somewhere. There's no reason to think he won't be a perfectly adequate, maybe even above-average outfielder once he gets up to speed, but how quickly will that happen? Ford is operating on a condensed timeline for a genuine World Series threat in the AL West, with the division crown still in reach. He will feel the heat.
4. 1B Jac Caglianone, Kansas City Royals
The Kansas City Royals' postseason dreams are on razor-thin ice, so we can't really expect Jac Caglianone to push deep into October, if at all. But he will be under the microscope over the next month as Royals fans (and the front office) start to flesh out expectations for next season.
When the towering 22-year-old was initially called up, expectations were high. Extremely so. Caglianone was borderline unfair against minor league competition, belting home runs left and right with a swing that had even the shrewdest MLB experts dreaming of Aaron Judge. The lefty certainly looks the part of a game-changing hitter, but so far the results are lacking.
Caglianone has a .145 average and .484 OPS with five home runs and 10 RBI across 152 at-bats in the Majors. He is straight up one of the worst hitters in baseball right now. He can still get behind a swing and belt one, but when he's not showcasing his immense natural power, Caglianone is almost exclusively striking out or finding a glove.
As someone who isn't going to provide a ton of value on defense, the Royals need Caglianone to hit. Kansas City's desperately lacks that big bopper to hit behind Bobby Witt Jr. and elevate a stagnant offense. While it's far too early to panic in any serious way about Caglianone — he's at the age when most prospects are just wading into Single-A or Double-A — the Royals certainly expected better than whatever this is.
A strong final month would help Royals fans put Caglianone's early struggles in the past and look forward with anticipation. If he continues to hack at air, however, doubt will naturally begin to creep in.
3. 2B Jackson Holliday, Baltimore Orioles
After an inconsistent rookie campaign, the Baltimore Orioles committed full stop to Jackson Holliday this season. He has been hitting at the top of the lineup for a while now, even if the results aren't fully in line with expectations for a leadoff bat. Holliday is coming off a fallow month of August, in which he hit .184 with a .600 OPS, but the overall numbers this season are much more palatable. He's hitting .276 with a .706 OPS and a 97 OPS+, hovering right around the league average.
Holliday is clearly an exceptional talent, and it's worth emphasizing just how impressive even "average" production is from a 21-year-old with the weight of MLB history foisted upon him. Sure, Holliday isn't going on the same early-career blitzkrieg that past superstars like Juan Soto or Manny Machado did, but he's flashing big-time upside. With 16 home runs and 14 stolen bases, you don't need to dig deep to find the potential for future 30-30 seasons once Holliday is fully acclimated and in tune with his abilities.
That said, because of his last name and because of all the hype that followed Holliday through the Minors and to the Orioles roster, he will feel the pressure to kick it up a notch in September — even with Baltimore's postseason hopes dead in the water. Folks aren't watching the O's to see if they win games. Folks are watching to see what Holliday, Samuel Basallo and this next generation can provide.
This has been a nightmare season in Baltimore, front to back, but next season will bring about new expectations. Adley Rutschman's name has already come up in trade rumors. The next wave of young talent in Baltimore has just about arrived. For a team with so much to look forward to, Holliday is still the foundation upon which everything else rests. The O's will not reach their ceiling until Holliday does.
2. RHP Nolan McLean, New York Mets
Through four starts, Nolan McLean looks like the New York Mets' new No. 1 starter. He has a 1.37 ERA and 0.76 WHIP with 28 strikeouts in 26.1 innings. As New York recovers from various injuries to the pitching staff, McLean has emerged as their white knight — a potential rotation savior who could lead the Mets deep into October.
That said.... we don't want to pin too much on 24-year-old with so little experience, right? So often pitchers come into the big leagues with guns blazing and string together a few stellar outings, only to hit a brick wall once MLB hitters "figure them out." Paul Skenes was the exception to the rule, but Mick Abel, Jacob Misiorowski and others pepper a long list of immediate pitching stars who couldn't sustain their early success.
New York seems destined to pin significant postseason starts on McLean. It will depend heavily on what happens over the final month. If he puts together a few more starts of this caliber, playing effortlessly between his mid-90s heat and a comically evasive sweeper or curveball, then the Mets might as well trot him out in Game 1 of the Wild Card round. But if McLean can't keep it up — if he starts to show even the slightest sign of rookie wall-hitting — it will leave the Mets and their rotation in a tough spot.
New York's rotation is basically split between unproven prospects and hurt or struggling veterans right now. There isn't a clear, proven ace to carry the mantle into October. So while McLean looks plenty dominant now, there is a ton of pressure to avoid the pitfalls so many other young pitchers run into.
1. RHP Jacob Misiorowski, Milwaukee Brewers
When 'The Miz' made his midseason debut, the entire baseball-watching world was swept up in imagination. He was unhittable for weeks, becoming the fastest player in MLB history to "earn" an All-Star berth. Jacob Misiorowski heard his name tossed around in the same conversation as Paul Skenes, viewed as the next great National League ace.
That may still be the case, but Misiorowski has hit that aforementioned rookie wall. The league has figured him out, and the results have been dire of late. He has allowed three-plus runs in five straight starts and he hasn't gone deeper than five innings during that stretch. He's up to a 4.50 ERA and 1.15 WHIP through 11 starts, notching 69 strikeouts in 48.0 innings.
There shouldn't be any long-term panic in the Milwaukee Brewers clubhouse. Misiorowski is still racking up swing-and-miss. His long stretch and unique release point, paired with triple-digit heat, makes him extremely difficult to hit when the command is on. He's not locating pitches right now, but he's 23. He has plenty of time to right the ship.
For Milwaukee, however, patience is running thin when it comes to the 2025 campaign specifically. The Brewers are the No. 1 seed in the National League with a comfortable lead and an impressively deep roster. As things stand, Misiorowski probably slides to the bullpen in October, where he can really play up his stuff before rejoining the rotation in 2026.
That feels like a disappointing outcome for a so-called All-Star like Misiorowski, though. If he can get back on the saddle over the final month, there's a world in which he's picking up key starts en route to a World Series. As things stand, however, 'The Miz' is on the brink of a demotion.