Man, this list got a lot worse up top this year -- thanks to the graduations of Manny Machado and Bryce Harper, among others -- since its most recent iteration. Nevertheless, the depth here goes well beyond 25 names and could easily run 40 deep before we're getting to guys who don't necessarily project as regular position players or average starting pitchers.
This list is limited to players whose seasonal ages for 2018 are 24 or younger -- that is, any player who will not yet have turned 25 by July 1, 2018 -- and who have exhausted their rookie status. That means no Harper or Machado (both are already 25) and no Ronald Acuna Jr. or Juan Soto (they haven't exceeded their rookie status yet).
1. Francisco Lindor: I'm still shocked by the power Lindor has shown the past year-plus in the majors -- granted, in a period when we know the ball itself is traveling farther -- and it's enough to elevate him to the top spot here, along with his plus defense and added value on the bases. However, you could make a great case for the guy right behind him.
2. Carlos Correa: Since the start of 2017, Lindor has posted 10.2 WAR and 10.1 fWAR (or, per Baseball-Reference’s version and FanGraphs’), versus 9.1/7.5 for Correa, but Correa has missed more than 50 games in that span, and on a rate basis has outhit Lindor, with a higher wOBA and wRC+. I think Lindor is a little more valuable because he's a plus defender at short, while Correa is fringy, maybe below average if you figure he's getting a boost from the Astros' heavy defensive positioning work. But it's really nitpicking -- they're both superstars, and if you want to put Correa at No. 1, go right ahead.
3. Alex Bregman: On bat value alone, Bregman is fourth among all eligible position players at all positions since the start of 2017, behind the two shortstops and Cody Bellinger. The two major advanced defensive metrics agree that Bregman is a below-average defender at third base, but the two positions he might play well -- shortstop, his natural spot, or second base, where his skills would likely land him on most teams -- are rather well filled right now in Houston. I've bumped him up a little because I think in the abstract Bregman is someone's All-Star second baseman, and probably worth more than what he has been able to provide Houston -- which, at 6.6 WAR since the start of last year, is still a lot.
4. Gleyber Torres: I might be getting ahead of myself, but I thought Torres was going to be a star, and he has been better than I expected, also in the power department. (Insert thinking face emoji.) Torres started the year in Triple-A, coming back from Tommy John surgery on his non-throwing arm, and was in the majors three weeks later; since then, he has hit .286/.346/.545 with a .323 BABIP that doesn't feel at all unsustainable given his bat control and the hard contact he makes. He's playing second base, which is fine but a waste of his talents; he's a true shortstop, a potentially above-average or better one, and if Didi Gregorius' cold stretch continues, I wonder whether he'll get a chance to move there in time.
5. Luis Severino: The development of Severino's slider from a third pitch in his arsenal to maybe the best slider in baseball has made him the clear No. 1 pitcher in the under-25 category -- no one else is close, not in production, not really in stuff, and to find anyone close in areas such as strikeout rate you have to include relievers. His changeup, which was his best pitch when he was still a prospect, has been oddly less effective this year, but that could just be small-sample-size variance. As long as he stays healthy, he's a No. 1 starter.
6. Corey Seager: This is Seager's last year of eligibility, and of course he won't play another game until next year after Tommy John surgery on his throwing elbow. He was third in the NL MVP voting two years ago off a huge rookie year that FanGraphs had at 7.0 WAR, and followed up with a great second season despite the tear in his elbow that required surgery this spring. I'm betting he'll return to be a five-WAR player regularly, probably more, but I bumped him down a few spots because he's not playing right now and most of these guys are.
7. Shohei Ohtani: Well, who really knows at this point? Ohtani generated two wins of value without even passing the rookie limits for at-bats or innings (though he has more than 45 days on the 25-man roster, so he has lost his rookie status via that technicality), and that probably understates what he was worth because he could fill two roles while occupying only one roster spot. But now he's out with a Grade 2 UCL tear, might need Tommy John surgery -- it seems as if now we're just postponing the inevitable, although I'd love to be wrong -- and it's possible he is done until the spring of 2020. Were he still healthy right now, Ohtani would have had a great case to be ranked No. 3 behind the two superstar shortstops on this list.
8. Andrew Benintendi: Benintendi is quietly breaking out this year, on track to surpass his offensive production from all of 2017 before this year's All-Star break. He's an above-average defender in left who's capable of playing average defense in center, which might be his long-term position if the Red Sox turn the page on Jackie Bradley Jr.
9. Cody Bellinger: Even with just a .246 batting average so far this year, Bellinger is still valuable because he walks, hits for power and is an elite defender at first base who also plays solid defense in center field. The 2017 NL Rookie of the Year won't turn 23 until July, so although he still has some holes at the plate -- which were exploited by Houston in the World Series -- there's also time for him to make adjustments.
10. Byron Buxton: Buxton has accumulated just 90 at-bats this year around multiple injuries, but he bounced back from a similarly awful start to 2017, after the Twins persuaded him to abandon an exaggerated leg kick, to post a 5.2 WAR season built on his grade-80 defense in center, his above-average offense and a 29-for-30 success rate on the bases.
11. Jose Berrios: Berrios remains a little homer-prone but has seen his control take a big leap forward this year, as he's averaging a walk every six innings (15 walks in 14 starts) and even missing bats a little more than he did in 2017.
12. Albert Almora Jr.: Almora's breakout this year is driven largely by a jump in his BABIP to .384, third highest in the majors this year and probably not likely to last, but he's a 70-grade defender in center and has become disciplined enough to be a credible leadoff option for the Cubs.
13. Addison Russell: Russell just hasn't developed at the plate as I anticipated. He's putting the ball in play more, getting on base at a good clip and hitting for more average, but with very little power and a lot more weak contact than he should, given his hand strength and bat speed. Even with that underdevelopment, he's still on track for a 3-4 WAR season as a superb defender at short with OBP skills.
14. Dansby Swanson: Swanson is striking out a lot more often this year but is doing more on contact, already matching his 2017 homer total in just 56 games. Of greater concern is that he has become almost a hacker, with a walk rate below 4 percent when he's not batting eighth (and thus just ahead of the pitcher).
15. Josh Hader: Through June 17, Hader had the highest strikeout rate of any season in which a pitcher threw at least 30 innings; just two pitchers have ever crossed 50 percent before, and Hader is on pace to face more batters than either of those guys did. Lefties are 3-for-42 off him with 27 strikeouts and six walks. Reliever peaks can be short and unpredictable, but few peaks have ever been quite this high.
16. Ozzie Albies: Albies' home run binge to start this year was about as big an outlier as you'll see in baseball -- he had 16 home runs total in his minor league career in 1,744 plate appearances, plus six homers last year in the majors in 244 PA, and hit his 16th homer of 2018 on June 12. Yeah, the ball is juiced, but it's not propelled by jet fuel. Unfortunately Albies' overall performance hasn't been good since his huge April -- his OBP since June 1 is .291 -- and it's possible that in trying to hit the ball out of the park he's surrendering some of what made him a good prospect to begin with, his ability to make hard line-drive contact to all fields and hit for average. He's an above-average defender at second who played short in the minors and in theory could return there. At 21, he's among the youngest players on this list, so I'm still bullish on him long term.
17. Paul DeJong: The incredible part of DeJong's story is that he has become a capable shortstop -- more than that, really -- despite playing just 11 games there in the minors and barely even playing the position in college. (In 2015, his junior year at Illinois State, he started at four spots, including catcher, but not shortstop, according to the ISU site.) He's a modern hitter -- a huge strikeout rate, but his contact tends be hard-hit and he produces power like few shortstops do. He just made the cutoff for this list, turning 25 in August, 32 days after the threshold for inclusion.
18. Nomar Mazara: Mazara made my breakout candidates list for this year, and so far he is fulfilling that promise, with 14 homers already (six off his 2017 total), doing more damage against lefties and showing better results against off-speed stuff as well. Let's hope the wrist soreness currently bothering him isn’t a long-term issue.
19. Rafael Devers: Devers has had some struggles at the plate this year, but bear in mind that he's just 21, younger than Alec Bohm, whom the Phillies took third overall in this month's first-year player draft, and already has 22 homers in the majors. Devers posted a .338 OBP last year at age 20 in 240 PA. The list of players who posted at least a .320 OBP at age 20 or younger, with at least 200 plate appearances, since 1980, includes 18 players, seven of whom have won MVP awards, with the worst players on the list still quite good -- guys such as Starlin Castro and Elvis Andrus. I'm still very bullish on Devers becoming a star at the plate.
20. Walker Buehler: Buehler just crossed the 50-inning career mark to qualify for this list, and he was worth more than a win this year in just a handful of innings before he went on the DL with a microfracture to one of his ribs. He works with above-average command of three above-average pitches, and his changeup isn't too bad, either. He just has no real history of staying healthy, so it's unclear what kind of workload he can ultimately handle in a rotation.
21. Lance McCullers Jr.: He's outstanding when healthy, with a curveball that's among the best in the game, but has missed huge portions of the past two seasons and still has trouble repeating his arm swing enough for average fastball command.
22. Miguel Andujar: He has been overshadowed by Gleyber Torres and included in every Yankees fan's trade proposals ("I wouldn't give up Torres for Trout, but I might include Andujar"), but he has still been a productive hitter with a high contact rate and above-average power. His defense has graded out poorly in a small sample, and he'll probably never be more than a fringy defender at third, but if he hits for average and power like this, he'll be more than just an every-day player, whatever uniform he wears.
23. Joey Gallo: Still the most raw power I've ever personally scouted on an amateur player. He's the new Rob Deer -- walks, strikeouts, enormous home runs -- and there's a nonzero chance he has an Aaron Judge-like breakout in his late 20s, as Judge himself did, by further tightening his command of the strike zone.
24. Yoan Moncada: Not as good as the hype, but still a good player, with the athletic ability to become more as he gets older. He has shown good range but been error-prone at second base; with the drafting of second-base prospect Nick Madrigal earlier this month, the White Sox might face a situation in which they have to consider moving Moncada to another spot, and his speed should play nicely in center field.
25. Ian Happ: Walks, homers and the ability to play (or fake) six positions all make him a potentially valuable player -- but he's striking out nearly 40 percent of the time this year, way up from last year's already-high 31 percent. He runs deep counts, so it's not as if he's overmatched, but his current whiff rate of 37.8 percent would be the highest ever in a full season for a player with even 300 PA if he doesn't bring it down.
Honorable mentions: There were way too many guys in this next tier after the top 20 or so, and you could easily make cases for players such as Edwin Diaz, Harrison Bader, Matt Olson, Jeimer Candelario, Ketel Marte, Manuel Margot and others.