Checking in on 2024’s reliever-to-rotation experiments

The 2023-24 offseason saw several teams go outside the box to add to their rotation mix by announcing plans to convert an established reliever into (or back into) a starting pitcher. It’s not a new concept by any means, but it’s always notable when a player who’s found some success in one pitching role is shifted to the other.

In some instances — e.g. Jordan Hicks, Reynaldo Lopez — the pitchers in question signed lucrative multi-year deals as part of this planned pivot. For others, this role change comes amid their original six seasons of club control and could greatly impact their earnings in arbitration and/or in free agency down the road.

Now that we’re about a quarter of the way through the year, it seems like a good time to check in on how some of these role changes are playing out. Readers should note that this rundown will focus on pitchers who pitched exclusively or near-exclusively out of the bullpen last season. Pitchers like Boston’s Garrett Whitlock (who started 10 games last year and nine in 2022) or Tampa Bay’s Zack Littell (who moved to the rotation last summer and finished out the ’23 campaign as a starter) aren’t the focus here so much as arms who were more strictly confined to short relief recently.

Since so many of these transitions are going to bring about clear workload concerns, we’ll check back in periodically throughout the season. For now, here’s how things are going through about 25% of the schedule.

Jordan Hicks, RHP, Giants

Hicks’ transition from flame-throwing late-inning reliever to … well, flame-throwing starting pitcher has gone seamlessly thus far. It’s only nine starts and 48 innings, but the 28-year-old boasts a 2.44 ERA in his move to the rotation. A career-low 19.9% strikeout rate is a red flag, but Hicks’ 8.2% walk rate is lower than the league average and a career-best mark as well. His 56.2% grounder rate isn’t quite as high as the 60% mark he carried into the season but is still more than 10 percentage points above average.

As one would expect, Hicks’ blazing sinker has lost quite a bit of velocity now that he’s not throwing one max-effort inning at a time. His sinker sat at 100.2 mph last year but is clocking in at 96 mph in 2024. Even with four fewer miles per hour on his primary offering, however, Hicks has more than enough velocity to keep hitters off balance.

Hicks has also fully incorporated the splitter he tinkered with in 2023 into his arsenal this year. After throwing it just 1.6% of the time last season, he’s thrown 22.5% splitters in 2024. Opponents may as well not even bother swinging at the pitch. Hicks has finished off 42 plate appearances with a splitter, and hitters have posted a .079/.167/.105 slash in those instances. Opposing batters have chased the pitch off the plate at more than a 35% clip, and Hicks boasts a huge 42.9% whiff rate on the pitch, per Statcast.

The big question for Hicks, as it is for virtually any pitcher making this transition, is how his arm will hold up once he begins pushing it into uncharted waters. Hicks has never topped 77 2/3 innings in a big league season. That mark came way back in his 2018 rookie showing. The 105 frames Hicks tallied as a minor league starter in 2017 are the most he’s ever pitched in a full season. He’ll be approaching his MLB-high after he makes another four starts or so and will be on the cusp of a new career-high about 10 to 11 starts from now — when there’s still roughly half a season left to play. Hicks wasn’t even especially durable as a reliever, only surpassing 35 appearances in two of his five prior big league seasons. The early returns are outstanding, but the real test will probably come in late June and into July.

Reynaldo Lopez, RHP, Braves

Unlike Hicks, Lopez is no stranger to starting games at the MLB level. He started 73 games for the White Sox from 2018-20 after coming over from the Nationals alongside Lucas Giolito and Dane Dunning in the Adam Eaton trade. The first of those three seasons went well, but Lopez stumbled in 2019-20 and began to transition to the bullpen in 2021.

The shift to a relief role seemed to suit the right-hander well. His already impressive velocity played up even further. Lopez averaged better than 95 mph as a starter in ’18-’20 but saw that number jump to 97.1 mph in 2022 and a massive 98.4 mph in 2023. Over those two seasons, he pitched to a sharp 3.02 earned run average. His rate stats were somewhat uneven, as he showed pristine command (4.3% walk rate) but an only slightly higher-than-average strikeout rate in ’22 before jumping to a huge 29.9% strikeout rate in ’23…but pairing it with a bloated 12.2% walk rate. Taken together, however, Lopez gave the Sox 131 1/3 innings with that 3.02 ERA, 31 holds, six saves, a 27.4% strikeout rate and an 8.5% walk rate.

When he signed with the Braves for three years and $30M, that generally fell in line with expectations for what he’d command as a late-inning reliever. However, it quickly became clear that the Braves were going to stretch Lopez back out. There was plenty of skepticism — myself very much included, admittedly — but the experiment has gone better than anyone could’ve imagined.

Thus far, Lopez has not only been the Braves’ best starter but one of the most effective starters in the league. He’s pitched 35 1/3 innings of 1.53 ERA ball. His velocity has dipped back down to his 2018-20 levels, sitting 95.6 mph, but that’s to be expected working out of the rotation. His 25.5% strikeout rate is better than average but not elite. His 9.9% walk rate could stand to come down. But Lopez is throwing more curveballs than ever before (10%), has largely abandoned his changeup and is keeping the ball on the ground at a career-best 41.1% rate. That’s a bit shy of the 42.8% league average but noticeably higher than the 35% clip he posted during his time with the White Sox.

The uptick in grounders is one reason that Lopez is yielding a career-low 0.51 homers per nine innings. The other is a 5.4% homer-to-flyball rate that he almost certainly can’t sustain. That fluky HR/FB and an abnormally high 88.7% strand rate are part of the reason metrics like SIERA (3.87) and xFIP (3.79), which normalize HR/FB, tend to peg him for some regression. Still, even if he’s bound to see his ERA tick up by a couple runs, Lopez has looked great through his first six turns.

Time will tell just how his arm can handle a return to his 2018-19 workloads, but the early results are excellent — and the importance of his breakout is magnified by the loss of ace Spencer Strider to season-ending elbow surgery. Notably, Lopez exited last night’s start with some tightness in his back, but manager Brian Snitker suggested after the game that he’s likely to make his next start.

A.J. Puk, LHP, Marlins

On the other side of the coin, the Marlins’ efforts to move Puk back into a starting role quickly went down in flames. Puk, a former No. 6 overall pick who worked as a starter in the minors, looked excellent this spring. He pitched 13 2/3 innings over four starts and two earned runs with a 23-to-4 K/BB ratio. The transition could hardly have gotten out to a more promising start.

In his first four regular-season starts, Puk also pitched 13 2/3 innings. The similarities stop there. Opponents bludgeoned Puk for 14 earned runs on 19 hits and a stunning 17 walks. He fanned only 12 of his 77 opponents (15.6%).

Miami placed Puk on the injured list on April 20 due to left shoulder fatigue. He returned from the injured list just yesterday. Despite myriad injuries in their rotation, the Fish have already pulled the plug on the rotation experiment for Puk, announcing that he’ll be back in the bullpen following his stay on the injured list. It’s a role he thrived in over the past two seasons, logging a 3.51 ERA, 29.4% strikeout rate and 6.9% walk rate while piling up 22 saves and 19 holds.

If Puk returns to form as a reliever — he was particularly impressive in ’23, striking out 32.2% of opponents against a 5.4% walk rate — the ill-fated rotation gambit will be little more than a footnote in what hopefully ends up as a strong overall career as a reliever. If Puk’s struggles persist, however, there’ll be plenty of second-guessing the decision to take one of the team’s best relief arms and stretch him out despite a litany of injury troubles that had combined to limit Puk to only 147 2/3 innings in his entire career prior to this season.

Garrett Crochet, LHP, White Sox

Crochet has worked to a pedestrian earned run average on the season due to a bevy of home runs allowed, but the former first-rounder who’s drawn comparisons to Chris Sale since being drafted by the White Sox has turned in elite strikeout and walk numbers. The 4.63 ERA looks unimpressive, but Crochet has fanned more than a third of his opponents (34.2%) against a pristine 4.8% walk rate.

Crochet boasts an excellent 14.5% swinging-strike rate and is averaging 96.9 mph on his heater. That’s a ways from the 100.2 mph he averaged in six innings as a rookie in 2020, but Crochet has had Tommy John surgery since that time and is working in longer stints now as opposed to bullpen work in ’20. This year’s velocity actually slightly exceeds his average velocity from working purely as a reliever in 2022-23.

In terms of workload concern, Crochet is up there with Puk in terms of extreme uncertainty. He entered the season with a total of 73 big league innings since his No. 11 overall selection in 2020 and is already at 46 2/3 innings on the young 2024 campaign. So long as he keeps missing bats and limiting walks anywhere near his current levels, the run-prevention numbers will come down — FIP and SIERA peg him at 3.33 and 2.37, respectively — but it’s anyone’s guess as to how Crochet will hold up. He skipped the minor leagues entirely, so even if you add in his whole minor league body of work, that’d only tack last year’s 12 1/3 rehab innings onto his track record. Going from a total of 85 1/3 professional innings over a four-year period to a full starter’s workload is bound to have some bumps in the road, but so far Crochet looks quite intriguing as a starting pitcher.

Jose Soriano, RHP, Angels

The Angels nearly lost Soriano back in 2020, when the Pirates selected him in the Rule 5 Draft. At the time, Soriano was wrapping up his rehab from 2020 Tommy John surgery and could’ve been stashed in a rebuilding Pittsburgh bullpen upon his reinstatement from the injured list. A setback in his recovery early in the season prompted another wave of imaging and revealed a new tear, however. Soriano underwent a second Tommy John surgery on June 16, 2021. He was eventually returned to the Angels.

Unfortunate as that back-to-back pair of surgeries was, Soriano’s injury troubles allowed the Angels to keep him in the system. They’re now reaping the benefits. The flame-throwing righty made 38 relief appearances last season and pitched to a quality 3.64 ERA with a huge 30.3% strikeout rate — albeit against a troubling 12.4% walk rate. Soriano averaged 98.6 mph on his heater last year and wound up picking up 15 holds, as the then-rookie righty increasingly worked his way into higher-leverage spots.

The Angels announced early in spring training that Soriano would be stretched out as a starter. His ramp-up continued into the regular season. His first two appearances this year came out of the bullpen but both spanned three innings. He’s since moved into the rotation and has looked quite impressive. Through his first seven starts, Soriano touts a 3.58 ERA with an above-average 24.8% strikeout rate and an outstanding 62.8% ground-ball rate. Even though he’s working in longer stints, he’s improved his fastball and is now sitting at 99.3 mph with it. His 12.4% walk rate still needs improvement, but the returns here are quite promising.

Soriano only pitched 65 1/3 innings between the minors and big leagues last year, and he’s already at 38 2/3 frames on the 2024  season. He’s never pitched more than 82 1/3 innings in a professional season. We’ll see how he fares as he pushes past those thresholds, but there’s a lot to like with this rotation move — even though it’s garnered far less attention than some of the others around the game.

Tyler Alexander, LHP, Rays

The Rays obviously have a knack for finding hidden gems and converting unheralded arms into viable starting pitchers — hey there, Zack Littell — and Alexander is an example of their latest efforts to do so. The left-hander has started for the Tigers in the past and functioned in a swingman role, but the Rays picked him up in a low-cost move following a DFA in Detroit with the idea of stretching him out. Since it’s Tampa Bay, not all of Alexander’s “starts” have been, well, actual starts. He’s followed an opener on multiple occasions already, but he’s followed that one- or two-inning table-setter with at least four innings each time out.

Overall, Alexander has made eight appearances and averaged just under five frames per outing (39 2/3 total innings). He’s sitting on a pretty rough 5.45 ERA, thanks in part to a six-run drubbing at the hands of the Yankees last time out (though he did at least complete seven frames in that start, helping to spare the Tampa Bay bullpen). Alexander’s 19.1% strikeout rate is about three percentage points shy of average. His 6.9% walk rate is about two points better than average. However, he’s taken his longstanding status as a fly-ball pitcher to new heights in 2024, inducing grounders at just a 30.4% clip.

Alexander’s 14.5% homer-to-flyball ratio is only a couple percentage points north of average, but because of the sheer volume of fly-balls he’s yielding, he’s still averaging more than two taters per nine frames. Opponents have posted an ugly 11.8% barrel rate against him (ugly for Alexander, that is). If he can’t cut back on the fly-balls and/or start finding a way to avoid the barrel more regularly, it’s going to be hard for Alexander to find sustained success. The Rays don’t convert on every dart-throw — much as it’s fun to joke to the contrary — and so far the Alexander experiment hasn’t paid off.

Bryse Wilson, RHP, Brewers

Wilson’s move to the rotation wasn’t necessarily planned, but injuries up and down the Brewers’ staff forced the issue. Five of his past six outings have been starts and he’s sporting an eye-catching 1.78 ERA in that span. The rest of the numbers in that stretch are less impressive. Wilson has a tepid 17.3% strikeout rate in that stretch but has walked an untenable 13.5% of opponents. Opponents have posted a hefty 45.7% hard-hit rate (95 mph or more) against him during that time. Were it not for a .191 BABIP and 92.2% strand rate, the ERA wouldn’t look nearly as rosy. Metrics like FIP (4.64) and SIERA (5.34) are quite bearish.

Wilson is still scheduled to take the ball on Saturday in Houston, but his recent stretch of run-prevention doesn’t seem sustainable without some improvements in his K-BB profile.