I typically update my ranking of the top MLB players under age 25 once a year, but with playoff rosters loaded with young talent, a year ago I started producing a special, shorter edition highlighting the top young players on postseason teams, and I'm doing so again for another youth-infused 2018 postseason field.
I use seasonal ages here, so to be included a player had to be 24 years old or younger on July 1.
An interesting fact: The top five hitters under 25 by FanGraphs' WAR are all in the playoffs, and nine of the top 12 are either on playoff teams or a team that just missed (the Cardinals, with two). Make sure you're sitting down for this, but it turns out having very productive young hitters in your lineup appears to be a good thing for your playoff chances. Go figure.
Alex Bregman & Francisco Lindor
Lindor and Bregman have quite a bit in common: Both were amateur shortstops, considered somewhat undersized and expected to hit for average but not for power, yet both reached 30 homers this year without losing anything else from their offensive profiles. Lindor is the better defensive player, a plus glove at shortstop with tremendous instincts, while Bregman has done a credible job playing out of position at third, with defensive value a little below average by defensive runs saved and UZR. They're far and away the two best under-25 players on postseason rosters, and you could pick either to be No. 1 overall, but I'd give the nod to Lindor because of how much he contributes in the field and the difficulty of finding that kind of offensive production from a shortstop.
The presumptive National League Rookie of the Year has had a huge second half -- .302/.403/.625, with a ridiculous 46.7 percent hard-hit rate per FanGraphs -- to likely seal up the award, and he won't even turn 21 until December, making him the youngest player on this list. He's done so playing left field most of the season even though he's a natural center fielder, and might be even more valuable in future seasons if and when he gets to return to the middle of the field. That skill gives him a little more value to Atlanta if Brian Snitker wants to sit Ender Inciarte or double-switch him out of a game to get some more thump in the lineup.
Benintendi had a quiet breakout this year, with his best offensive performance since he reached the majors, including 41 doubles and 70 unintentional walks, both career highs, and the best defensive showing of his career as well. He's still somewhat vulnerable against left-handed pitching, trading some of 2017's walks for much greater power against southpaws.
You probably know the story by now: Buehler underwent Tommy John surgery right after the Dodgers drafted him, worked on conditioning during his rehab, added a lot of muscle and came back throwing harder than he ever had before. He'll hit the mound with two plus pitches on any given night and might show you a third. He's now thrown more innings in the majors (146⅔) than in the minors (109⅔) and is at 153⅓ total pro innings this year. That is by far the highest workload he's had since high school, beating 115 innings in 2014 between Vanderbilt and the Cape Cod League, so fatigue has to be a concern for the Dodgers as they plan their October rotation -- even though Buehler's probably their second-best starter right now after Clayton Kershaw.
If we're talking about just for this postseason, it's hard to think of Severino as the pitcher he was from the start of 2017 until about the midpoint of 2018. He hasn't looked right since the All-Star break, with an ERA of 5.57 in the second half, some slip in his velocity, a bigger slip in fastball command and a lot of hard contact allowed. Of course, he was a top-five pitcher in the American League for the season and a half before that, and don't be surprised if that guy shows up in October -- perhaps if the schedule allows him some extra time between starts.
I wrote a bit about Marquez in my "players I was wrong about" piece, as he's managed to have a tremendous season for the Rockies -- not the easiest place to pitch -- despite the lack of a real changeup or other pitch to get left-handed batters out. If I were an opposing manager facing him in October, I'd try to load the lineup with lefties, since he was lights out against right-handed batters (.188/.254/.337, nearly 35 percent strikeout rate) all season even with the added burden of pitching at Coors Field.
Albies' huge start this year was a great story, and it's still rather amazing that a 5-foot-8 (if that) hitter with no history of power could hit 24 bombs in the majors this season ... but the second half of the movie didn't quite live up to the first, as he hit just four homers after the All-Star break with a .282 OBP. Fourteen of his homers came before June 1, and since then, he's been much less productive at the plate. He's only 21, and his future remains very bright, but if we're betting on October production here, I'd think of Albies as more of a contact hitter than a power guy and would probably bat him later in the lineup due to the lack of on-base ability at the moment.
Bellinger got off to a rough start this year, with his rate stats bottoming out on June 3, when he was hitting just .225/.298/.413; you might live with that in center field, where Bellinger played about half the time, but not at first base. Since that nadir he's hit .282/.371/.506, boosted by some intentional walks, and he is an elite defender at first who can handle any outfield spot if needed.
With Corey Seager out for the year, the Dodgers needed more production from Bellinger this season, and they've been getting it for four months now. He's still not very good against lefties, though, and I'd put him well down in the lineup when one starts for L.A.'s opponent.
You know how absurdly effective Hader has been this year, and if he can keep doing that in October, the Brewers will be very tough to beat unless their opponents put some crooked numbers up on Milwaukee's starters. Hader hasn't been quite so invincible near the end of this long season, however. He's given up two or more runs in just seven outings all year, but three of those came in the season's final four weeks, and those all involved at least one home run hit off Hader. I'm not saying this is predictive, just that he's fallible, and it's possible 81⅓ innings, well spread out over 55 appearances, might just be wearing him down.
Honorable mention: Lance McCullers Jr., Gleyber Torres, Miguel Andujar