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Nobody ever reads the intro, and that goes double when the intro is written to explain rather than entertain. But I must explain!

Specifically, I'd like to clarify three things.

  1. I'm using the term "call-ups" very liberally. You're probably envisioning prospects -- and some of them are indeed prospects -- but really, I'm talking about any player added to a major league roster on Sept. 1, when rosters expanded by two. It could be because they were activated from the IL. It could be because they were claimed by some other team. Several such players are likely of more use in Fantasy than true prospects, so why limit myself?
  2. Notice my verb choice in the headline. I'm saying these players could matter in Fantasy Baseball. I'm not saying they will. I'm not even saying they should. In fact, they probably won't. Many are limited in opportunity and even ability. Still, roster expansion gives me a chance to address some new names while satisfying the curiosity of the many who search "September call-ups" this time of year, and I'm happy to oblige in that way.
  3. There are some players who were added to rosters on Sept. 1 who may be of even more use than those mentioned here. Maybe Jake Burger goes on a home run binge. Maybe Chris Martin gets a chance to close out some games in conjunction with Shawn Armstrong. Maybe Luisangel Acuna steals a bunch of bases in a part-time role. But you don't need me to tell you that, right? The range of outcomes for these players is well known already, so I don't care to address them beyond the brief way I just did.

And with that, I give you 12 September call-ups who could matter in Fantasy Baseball, ordered loosely by my level of interest.

Sal Stewart, 2B, Reds

2025 minors: .309 BA (437 AB), 20 HR, 17 SB, .907 OPS, 46 BB, 77 K
2025 majors: 2 for 8, 2 K

This is the big one. As I wrote in my waiver wire article earlier this week, Stewart, who always stood out for his plate skills, really seemed to grow into power after his move up to Triple-A, homering 10 times in just 38 games at the minor leagues' highest level. His average and max exit velocities were both 93rd percentile or better. He struck out at just a 16 percent rate. He was glorious in all the ways that would vault a borderline top-100 prospect into the consensus top 50. The big question is where he plays, but he's gotten to start both games since his promotion at first base. Third base, second base and DH are also possibilities.

Jac Caglianone, 1B/OF, Royals

2025 minors: .337 BA (264 AB), 20 HR, 1.025 OPS, 31 BB, 57 K
2025 majors: .147 BA (150 AB), 5 HR, .485 OPS, 8 BB, 34 K

Yes, we've already seen Caglianone play some in the majors, and it didn't go well. But his hamstring injury came just as he was reaching the two-month mark, when things so often click for rookie hitters. The Royals slow-played his rehab assignment, allowing him to regain confidence at Triple-A while waiting for rosters to expand, and in 16 games there, he slashed .385/.467/.692 with five homers and just a 14.7 percent strikeout rate. Clearly, there's nothing for him to accomplish in the minors, and his massive power is sorely needed by a fringe playoff contender that ranks in the bottom five in home runs. It shouldn't surprise anyone if Caglianone comes closer to meeting his potential in his second big league stint.

Ha-seong Kim, 2B/SS, Braves

2024 majors: .233 BA (403 AB), 11 HR, 22 SB, .700 OPS, 58 BB, 77 K
2025 majors: .227 BA (88 AB), 2 HR, 6 SB, .629 OPS, 8 BB, 23 K

I told you not all of these "call-ups" were prospects. Kim has ample major league experience, but he's widely available in Fantasy and more interesting, at least in the short-term, than all but the two guys ahead of him here. That's all the more true with the amount of faith the Braves are showing in claiming outright from the Rays. He's all but certain to pick up his $16 million option for next year, given the way this year has gone -- first, a three-month recovery from offseason shoulder surgery, then two separate IL stints for back issues -- so they must view him as a substantial upgrade from Nick Allen. He's at least as good defensively and is proven to have 15-homer, 30-steal upside if he can stay on the field. The Braves give Kim more job security than he had with the Rays, who recently promoted prospect Carson Williams to play shortstop.

Hyeseong Kim, 2B/SS/OF, Dodgers

2025 minors: .268 BA (149 AB), 5 HR, 14 SB, .793 OPS, 13 BB, 42 K
2025 majors: .304 BA (138 AB), 2 HR, 12 SB, .744 OPS, 6 BB, 42 K

Well, this isn't confusing at all. From Ha-seong to Hyeseong, the younger Kim isn't as proven as the older one, nor does he have a position to call his own, but you see the work he was doing before being sidelined by shoulder bursitis. He hit .324 (11 for 34) with a double and triple on his Triple-A rehab assignment and appeared at shortstop, second base, center field and left field there, positioning himself as a potential fill-in all over the diamond. Given that the Dodgers currently have Miguel Rojas manning second base, it wouldn't take much for Kim to take over there full-time, though it's worth noting that Tommy Edman just began a rehab assignment for a sprained ankle. Kim's exit velocities and strikeout rate leave much to be desired, but production counts for something, too, particularly given his history in the Korean league.

Harry Ford, C, Mariners

2025 minors: .283 BA (374 AB), 16 HR, 7 SB, .868 OPS, 74 BB, 88 K

Among first-time call-ups, Ford rates second only to Sal Stewart, so the problem for him isn't so much capability as opportunity. After all, he plays catcher in the organization with the game's best catcher. Cal Raleigh has become a historic slugger and MVP candidate this year, and his defense makes him the team's preferred choice behind the plate as well. Ford, who's more athletic than the typical catcher, got some exposure to the outfield last year but hasn't made a single appearance there this year. So why even bother to list him here? Because I think he's the real deal, and his promotion is a tacit acknowledgement that he's a finished product as well. If the Mariners aren't moving on from Raleigh (and they're not), then they have to move on from Ford, and every successful at-bat down the stretch, even if not consistent enough for him to matter in Fantasy, improves his trade value in the offseason.

Carter Jensen, C, Royals

2025 minors: .290 BA (427 AB), 20 HR, 10 SB, .878 OPS, 60 BB, 122 K
2025 majors: 0 for 1, 1 K

Jensen's situation is similar to Ford's in two ways: His minor league performance completely justifies his promotion, and he's joining an organization with an all-timer at catcher already. The difference is that, unlike Cal Raleigh in Seattle, Salvador Perez has mostly outgrown the position, whether he knows it or not. Meanwhile, his previous understudy, Freddy Fermin, was moved at the trade deadline. Jensen has yet to enter the lineup for the Royals, and I'm skeptical he'll play enough to matter at what's become a loaded position in Fantasy. But he should be an impactful hitter when he is in the lineup, having averaged 94 mph on batted balls in his 43 games at Triple-A, and is likely the one who will eventually force Perez into a primary DH role.

Kevin Alcantara, OF, Cubs

2025 minors: .266 BA (379 AB), 17 HR, 10 SB, .819 OPS, 48 BB, 128 K
2025 majors: 1 for 3, 2 K

Part of me wonders if Alcantara's promotion was mainly to buy back the extra days Owen Caissie needs to retain rookie eligibility for next season. He's the more deserving of the two and was sent down in conjunction with Alcantara's promotion. But Alcantara is deserving in his own right and actually got a stint in the majors last year as well. Like Caissie, he's hindered by the Cubs having a full outfield already, but he did find his way into the lineup against a left-hander Tuesday, starting in place of the struggling Pete Crow-Armstrong. Though once a highly rated prospect, Alcantara never made the expected strides with regard to strikeout rate and launch angle. He wouldn't be the first athletic marvel, though, to put it all together at the highest level, provided he gets that chance.

If Kyle Tucker's calf injury, which he suffered Tuesday, ends up requiring an IL stint, maybe Caissie could come back and enter into a lefty/righty platoon with Alcantara.

Craig Yoho, RP, Brewers

2025 minors: 7 SV, 1.04 ERA, 1.02 WHIP, 43 1/3 IP, 20 BB, 55 K
2025 majors: 0 SV, 8.22 ERA, 2.22 WHIP, 7 2/3 IP, 9 BB, 5 K

Back in late April, when Trevor Megill was struggling, there was some momentum for replacing him with Yoho, who had just been promoted for the first time. But Yoho struggled in that stint and got sent back down while Megill ended up pitching his way into the All-Star game. Seeing now where Yoho's numbers ended up, the hype was justified. The 25-year-old has a best-in-its-class changeup, one that breaks even more than Devin Williams' airbender and is thrown just as liberally, and he's back at a time when Megill is sidelined by a flexor strain. Abner Uribe, now closing, has been an excellent setup man, but blew his latest save chance. Does that open the door for Yoho? Probably not, but he could position himself high in the pecking order for next year with a strong finish this year. Given how volatile relievers are, anything is possible from there.

Andrew Alvarez, SP, Nationals

2025 minors: 3-7, 4.10 ERA, 1.35 WHIP, 123 IP, 52 BB, 114 K
2025 majors: 5 IP, 1 H, 0 ER, 2 BB, 4 K

Alvarez has never rated as a prospect, really, but he's been a stable enough performer in the minors over the past five years and just debuted with five one-hit innings against the Marlins on Monday. He has some runway on a team with few true rotation commitments and is exactly the sort of pitcher that evaluators tend to overlook, lacking both velocity and a true put-away pitch but able to limit damage by keeping the ball on the ground. Chances are he's a streamer at best in this final month, but the odds are greater than zero that he turns into more, particularly since pitchers have always been harder to project than hitters.

Justyn-Henry Malloy, OF, Tigers

2025 minors: .317 BA (243 AB), 8 HR, .934 OPS, 50 BB, 62 K
2025 majors: .214 BA (98 AB), 1 HR, .638 OPS, 19 BB, 31 K

I've always liked Malloy, who works the count as well as any minor leaguer, having reached base at a .415 clip across five seasons there, and has always delivered the sort of pull rates that would ensure he maximizes whatever power he has. And that power seems to have improved this year, his max exit velocity climbing to 110.8 mph (79th percentile) while his other exit velocity thresholds all rate in the upper half of the league. Sure, his repeated chances in the majors so far, which have amounted to nearly 350 plate appearances altogether, have gone nowhere, but that leap from the minors to the majors has been an especially difficult one for hitters in recent years. As long as he's still getting chances, Malloy has a chance, and it sounds like he should get plenty of chances against left-handers down the stretch.

George Valera, OF, Guardians

2025 minors: .318 BA (151 AB), 7 HR, .938 OPS, 18 BB, 38 K
2025 majors: 0 for 1, 1 BB 

Back when Valera rated as a top-100 prospect, which was true for Baseball Prospectus for four straight years, his arrival would have been big news, but seeing as no publication has rated him as a top-100 prospect since preseason 2023, it's merely a footnote. That said, the 24-year-old has had a solid, if still injury-plagued, 2025, though it looks worse when you take out his 16 games at Rookie ball. He slashed .255/.346/.457 in his 28 games at Triple-A -- a modest line, but it came with high exit velocities, a high walk rate and even a cycle, which he hit for on Aug. 28. That combination of on-base ability and hard contact is what made Valera a highly regarded prospect in the first place, and he may not have fallen off that perch if not for a string of injuries. Given that the Guardians are forever in search of outfield help, he still has a chance.

Nick Yorke, 2B, Pirates

2025 minors: .287 BA (401 AB), 7 HR, 17 SB, .754 OPS, 36 BB, 97 K
2025 majors: 1 for 2

Nick Gonzales has played to a 0.0 bWAR this year, so anyone who tells you he has the Pirates' second base job on lockdown is mistaken. It's kind of surprising that Yorke has taken this long to come up in 2025, given that he made a strong impression last year, but his top-line production and exit velocities have both taken a hit at Triple-A this year, exemplifying the up-and-down nature of his entire minor league career. He clearly found his stroke in August, though, batting .337 (34 for 101) for the month, and should have ample opportunities down the stretch. He started at first base over Spencer Horwitz against a left-hander Tuesday and should also get looks in left field and, yes, at second base. While the impact potential of his bat is in doubt, he's always earned high marks for plate discipline.