2024 MLB Playoffs: 15 Young Stars Who Could Shape The Postseason
Image credit: Jackson Chourio (Photo by John Fisher/Getty Images)
Every postseason offers the chance for a young player to have a breakout performance on baseball’s biggest stage.
Some use the spotlight to announce their arrival earlier than expected, such as Andruw Jones in 1996, Francisco Rodriguez in 2002 and Evan Carter in 2023. Others, such as Miguel Cabrera in 2003 and Dustin Pedroia in 2007, continue building on their path to stardom.
With just two weeks remaining in the regular season, it’s a good time to profile the youngsters we could see make a name for themselves come this October.
Corbin Caroll, OF, Diamondbacks (Age: 24)
Carroll’s recent offensive eruption has fueled the D’-backs’ second-half surge. Arizona enters Tuesday’s action with the second-highest wRC+ in MLB and the most runs scored. The gap between the Diamondbacks (824) and the second-place Yankees (751) is nearly as big as the one between the Yankees and the Guardians (who rank 14th).
Carroll’s performance has been welcomed after a disastrous first half that led many to believe his nagging shoulder was beyond repair. Teams tell us how they feel about players with their actions, and it only took until April 24th for Carroll to be dropped to seventh in the order. At no point in 2023 did he hit that low against a right-handed starting pitcher.
There’s an entire offseason to dive into the shoulder mystery, but for now, the 24-year-old is back performing like a franchise hitter should.
In early August, SwingGraph’s proprietary vertical bat angle data showed that Carroll was taking steps to regain his 2023 swing:
Though his plate discipline worsened, finding a way to hit more fly balls unlocked his power. While not typically considered a power bat, only 11 hitters have hit more homers than Carroll since the All-Star break.
Gunnar Henderson, SS, Orioles (Age: 23)
BA’s former No. 1 overall prospect had a stellar start to his sophomore season, slashing .286/.373/.584 (169 wRC+) through the first half.
He’s been good since then — hitting .273/.357/.469 (137 wRC+), but his power output had a cold spell in July and August when Henderson wasn’t able to lift the ball quite as well:
As evidenced above, Henderson has begun putting the ball in the air more, and after “bottoming out” with a 104 wRC+ in August, he has once again been one of the best players in baseball in September.
By fWAR, Henderson is having the best year by an Oriole since Cal Ripken Jr. in 1991. Depending on how he finishes over the next two weeks, he could record a top five season for a Baltimore position player all-time.
Bobby Witt Jr., SS, Royals (Age: 24)
Part of the reason Henderson hasn’t received as much shine in the second half has been because of Witt, who has a 167 wRC+ to go along with elite defensive metrics. Since he has to one-up Henderson in this way too, we’ll note it’s the highest fWAR total ever recorded by a Royals position player:
Witt’s progression has gone as well as one could’ve hoped since his rookie debut:
- 2022: 2.3 fWAR, 98 wRC+
- 2023: 5.8 fWAR, 114 WRC+
- 2024: 9.7 fWAR, 167 wRC+
He’s done it by improving his barrel rate and taking far fewer called strikes, while his strikeout and walk rates have improved each season.
A year after losing 106 games last year, the Royals are well-positioned to reach the playoffs, and they’ll be led by one of MLB’s very best players once they arrive.
Jackson Chourio, OF, Brewers (Age: 20)
Many words have already been written about Chourio, who recently became the youngest player in MLB history to record a 20/20 campaign. BA readers should expect more about Chourio’s excellence as he closes in on a phenomenal first year in the majors, which will include some postseason experience before he can legally have a drink.
Chourio doesn’t yet possess excellent swing decisions. He chases outside the zone at a decent clip, but the key to his rookie year has been how quickly he has improved.
In April and May, Chourio combined a 35.5% chase rate with a 13.9% swinging strike rate. Those numbers have dropped to 30.5% and 10.1% since June 1. During this stretch, Chourio ranks 11th among all hitters in wRC+ and fWAR. He becam e a top-12 position player in baseball once he was able to make his adjustments.
It follows a familiar pattern of Chourio adjusting to his competition. Last season at Double-A, he had a .714 OPS with a 21 K% through the All-Star break. Afterward, which coincided with the Eastern League’s removal of the pre-tacked ball, he posted a .914 OPS with a 14% strikeout rate.
Further improvement could be coming in 2025. Perhaps it’ll begin as early as this year’s postseason.
Jackson Merrill, OF, Padres (Age: 21)
Merrill didn’t start the season as poorly as Chourio did, but he also hasn’t been as consistently excellent in the second half. Still, it’s impossible to say that his year has been anything but a 99th-percentile outcome for both him and the Padres.
Recall that Merrill’s season began with him becoming one of three players in the past 50 years to start in center field on Opening Day at age 20 or younger. The absurdity of that stat doesn’t even account for the fact that Merrill had only started five games in the outfield as a professional.
Not only does Merrill comfortably lead all rookies in fWAR this year, but similar to Chourio, he’s been one of baseball’s best hitters since the beginning of June, with a top-20 wRC+ during that span. He’s been clutch, too, ranking 22nd in Fangraphs’ win probability added metric. It’s an excellent sign for a red-hot Padres team getting set for postseason play.
Colton Cowser, OF, Orioles (Age: 24)
A strong candidate for American League Rookie of the Year honors, Cowser’s season has been quite uneven. He has two months with a wRC+ of 160 or above but has otherwise been below league average (or barely above it).
However, elite defense has kept Cowser’s name in Baltimore’s lineup throughout the summer, and he now ranks second on the Orioles in fWAR, as he has pulled ahead of Adley Rutschman and Anthony Santander.
Cowser’s near-31% strikeout rate could be an issue in the playoffs, but the possibility of him contributing a two-way impact can’t be ignored, which makes him one to watch in October.
Anthony Volpe, SS, Yankees (Age: 23)
Unfortunately for Yankees fans, Volpe’s season has had the opposite “shape” of Chourio and Merrill.
Through June 1st, Volpe was hitting .282 with a 20.5 K% and six homers. Since then, he’s batting .223 with a 24.2 K% and just five homers.
The 23-year-old had a goal not to pull as many fly balls this season, and he’s achieved that:
- 2023: 28%
- 2024: 18%
Overall, he has only slightly improved his wRC+ from his rookie campaign (82 last year to 87 so far this season).
The idea was to flatten his swing, hit for a higher average and use his speed on the base paths. The early returns were promising, but Volpe hasn’t been able to maintain the strong performance throughout the summer.
An optimistic view of the situation could be that Volpe has shown multiple approaches during his brief time in the bigs. Perhaps it all clicks in October, a la Jeremy Peña in 2022. Either way, it’ll be interesting to see which approach Volpe utilizes during the early part of 2025.
Michael Harris, OF, Braves (Age: 23)
Last season, Harris predictably rebounded from an injury-induced slow start. After looking like his usual self in April of this year, the Braves are still waiting for him to come around again:
His yearly wRC+ metrics show a troubling trend:
- 2022: 137
- 2023: 115
- 2024: 82
Since May 1st, Harris has been even worse, hitting .221/.265/.343 with just four stolen bases in 291 plate appearances. The critical issue is that he’s chasing outside the zone more than ever before while making less in-zone contact than ever before. A ground-ball rate that has ticked back over 50% isn’t helping either.
Still, the postseason represents fresh opportunities, and in a small sample, Harris’ skills could flash once again.
Mark Vientos, 3B, Mets (Age: 24)
Among all third basemen with at least 400 PAs, nobody has a higher wRC+ than Vientos. Among all position players, the 24-year-old breakout star has the 15th-highest mark in MLB.
It’s a remarkable transformation for a young hitter who seemed overwhelmed by big-league pitching in his first couple of attempts at the level. It has also been tremendous for the Mets, who have ridden a top-10 lineup and an upstart rotation into Wild Card contention.
Vientos has a 92nd percentile barrel rate through mid-September. His 29% strikeout rate, however, isn’t ideal, nor is a 15.6% swinging strike rate.
Making more consistent, hard contact, even when he isn’t barreling, is Vientos’ next step. He could begin working on it in October, should the Mets advance.
Riley Greene, OF, Tigers (Age: 23)
The Tigers enter Tuesday’s action just 1.5 games behind the Twins for the third and final American League Wild Card spot.
Since August 11th, Detroit’s 23-10 record is the best in the AL, led by the 9th-highest wRC+ offensively and the best ERA by any pitching staff. Specifically, the bullpen has been dominant, with a league-best 5.5% walk rate.
Yet ,the club wouldn’t have made it this far without Greene, who has improved at the plate in each of his three big-league campaigns. In 2024, he has done everything one would want a young hitter to do: increase his BB% and barrel% while cutting down on the strikeouts.
Chasing fewer pitches outside the zone has allowed Greene to lift the ball better. Should Detroit sneak into October, a lot will be made about the team’s bullpen, which is deserved. However, among Tigers position players with at least 300 PAs, Greene is one of two to have a wRC+ over 100, and his current 139 mark makes him a top-20 hitter in baseball.
Spencer Arrighetti, RHP, Astros (Age: 24)
It wasn’t a solid initial major league impression for Arrighetti, but he has drastically turned things around in the second half:
First, it’s worth noting that his 4.38 xFIP before the All-Star break shows he might not have been as bad as the ERA suggested. Blowup outings were an issue for the 24-year-old, as he allowed five or more runs in a start four times in the first half.
He entered the season as BA’s third-ranked Astros prospect, but he was far more unheralded than many of his first-year peers. Arrighetti still doesn’t rate well by a metric like Stuff+, but as he recently told Fangraphs’ David Laurila, he now leans into advanced data to focus on attacking hitters’ weaknesses.
With Justin Verlander suddenly looking like a 40-year-old pitcher, Arrighetti’s postseason presence could be more impactful than Houston ever would’ve imagined entering the season.
Spencer Schwellenbach, RHP, Braves (Age: 24)
Schwellenbach was recently highlighted in an early-August piece that hit on four rookies having underrated seasons.
This young arm is still adapting to being a full-time pitcher. While at Nebraska, he focused on shortstop, though he also displayed upper-90s velocity as the team’s closer. He needed Tommy John surgery after the 2021 draft and didn’t return until last season.
The key to his success is a vast arsenal with excellent command. Among pitchers with at least 100 innings this year, only 10 have a lower walk rate than Schwellenbach. Of those 10, only Tarik Skubal, Logan Gilbert and Joe Ryan have a better K-BB%. Schwellenbach’s 21.9% mark is slightly above Shota Imanaga’s, for context.
Ultimately, Schwellenbach’s contributions have kept Atlanta’s season from completely falling off the tracks. The club enters Tuesday sitting one game behind their rival Mets for the final Wild Card slot.
Orion Kerkering, RHP, Phillies (Age: 23)
Kerkering already introduced the world to his hellacious breaking ball last postseason, and now he’ll enter the 2024 playoffs with a full year of major league success under his belt.
Kerkering’s formula is simple: He has a top-30 K%, a top-25 BB% and a top-20 GB%. Strike batters out, limit the walks, and induce grounders. It adds up to the 11th-best SIERA among qualified relievers.
His multi-faceted approach to getting outs is also displayed in the quality of his arsenal. Per Baseball Savant’s run values, Kerkering’s three-pitch mix is balanced:
While his time as future closer hasn’t yet arrived, Philadelphia will still rely on him as a vital member of the bullpen in the 2024 postseason.
Justin Martinez, RHP, Diamondbacks (Age: 23)
Another reliever who could have a meaningful role this fall, Martinez is coming off a few rough outings and has allowed four earned runs in six September innings. This comes after a dominant August in which he posted a 1.88 ERA and became the closer for baseball’s hottest team.
Similar to Kerkering, Martinez excels at inducing grounders, as his 59 GB% is top-10 among qualified relievers. Unlike Kerkering, however, Martinez struggles with walks, which could be problematic in a short series.
The good news is Martinez’s xFIP has been essentially the same in September as it was in August. We’re dealing with microscopic samples in both cases, but it suggests that his recent struggles have been bad luck or perhaps mechanics-related. A 50% left-on-base rate is always challenging to overcome.
Arizona’s bullpen has been tremendous of late, but they’ll need Martinez to lock down the ninth inning as the club seeks a second straight National League pennant.
David Festa, RHP, Twins (Age: 24)
Similar to Arrighetti, Festa had a rough opening in the majors, allowing 12 earned runs across his first two starts.
Since then, the 24-year-old has logged nine appearances, totaling 58 strikeouts in 45 innings to go along with a 3.80 ERA. Matching 3.37 FIP and xFIP marks back this up.
He’s recorded more than 15 outs in a game just once in his big-league career, so Minnesota won’t be leaning on him too much if the team avoids a late-season collapse to secure the final AL Wild Card spot. Perhaps missing out on the national spotlight will help keep Festa’s fantasy ADP in check. He’s a name to monitor entering 2025.
