Shota Imanaga’s Hamstring Strain Magnifies Cubs’ Other Rotation Losses

While the Cubs are 22-15 and own a three-game lead in the NL Central — the largest of any team at this writing — the rotation that’s helped them to that perch has taken its hits recently. Last month, 2023 All-Star lefty Justin Steele underwent surgery to repair his ulnar collateral ligament, and Javier Assad suffered a setback while rehabbing to return from an oblique strain. And then on Monday, the Cubs placed 2024 All-Star lefty Shota Imanaga on the injured list due to a left hamstring strain. While his injury isn’t considered to be major, his loss could tighten the division race and test the depth of the already-depleted rotation.

After leaving his April 29 start against the Pirates after five innings due to cramps in both quadriceps, Imanaga cruised through the first five innings against the Brewers on Sunday in Milwaukee, allowing just three singles while striking out four without a walk. The 31-year-old’s afternoon ended on a sour note, however. With the game still scoreless in the sixth, he yielded a leadoff single to Jackson Chourio and then a one-out walk to William Contreras. It looked as though he might escape unscathed when he got Christian Yelich to ground to first baseman Michael Busch, who started a potential 3-6-1 double play. Imanaga ran to cover first base, but not only was Dansby Swanson’s throw a bit late, the pitcher came up limping, forcing him out of the game.

Reliever Julian Merryweather entered, threw a wild pitch that allowed Chourio to score from third, and by the time he got the final out, three more runs had scored in what ended as a 4-0 loss for the Cubs. They suffered a much more gruesome defeat on Tuesday, when reliever Ryan Pressly allowed eight straight Giants to reach base in what became a nine-run 11th inning and a 14-5 drubbing.

An MRI of Imanaga’s injured leg revealed a mild strain, and he was placed on the 15-day injured list. He’ll likely be out longer, as Cubs president of baseball operations Jed Hoyer told reporters, “The most important thing with that kind of injury is to get him back and healthy for the remainder of the season, not just to get him back. You talk about returning to play, versus returning to your previous form. That’s the most important thing, and it may take some time to get there.”

Through eight starts totaling 44 2/3 innings, Imanaga had generally been effective, in that his 2.82 ERA was slightly below last year’s 2.91 mark. However, both his 4.52 FIP and 4.58 xERA suggest he was walking a tightrope. Relative to last season, his first in the U.S. after a six-year run with NPB’s Yokohama Bay Stars, his strikeout rate had dropped from 25.2% to 18.8%, while his walk rate had risen from 4.0% to 7.7%. Meanwhile, his average exit velocity allowed has increased from 88.6 mph to 90.4, his barrel rate from 8.6% to 10.5%, and his pulled air rate from 22.5% to 24.1%.

One factor in Imanaga’s taking a step backward in those areas may be that he has lowered his arm angle from 40 degrees last year to 37 this year. The lower angle is supposed to create deception and increase the amount of arm-side run for his four-seam fastball (and it has, by nearly two inches). But the pitch has become much less effective when thrown in the upper third of the strike zone, where batters have improved their slugging percentage from .448 to .586 and their barrel rate from 13.2% to 22.2% — a trade-off not worth the gains in whiff rate (from 17% to 23.3%). Overall, batters are slugging .594 against his four-seamer this season, up from .471 last year; his Statcast run value on the pitch has plummeted from 4 to -7.

The Cubs have yet to determine who will fill Imanaga’s rotation slot, though on Monday manager Craig Counsell pointed to veteran Chris Flexen and prospect Cade Horton as the top options. Flexen, a 30-year-old righty, spent last season on the south side of Chicago, laboring as the top innings eater on the abysmal White Sox. He didn’t pitch as badly as his 3-15 record suggests, but his 4.95 ERA (122 ERA-) and 4.80 FIP (114 FIP-) were both subpar. Signed to a minor league deal by the Cubs, he made five starts for their Triple-A Iowa affiliate, posting a 1.16 ERA and 2.88 FIP in 23 1/3 innings, before being called up on April 30. He earned a three-inning save in his season debut on Friday, shutting out the Brewers on one hit and two walks while striking out four.

Now that he’s on both the 26- and 40-man rosters, Flexen has a leg up on Horton, a 23-year-old righty who was the seventh pick of the 2022 draft out of the University of Oklahoma. The 6-foot-1, 211-pound righty placed 64th on our updated Top 100 Prospects list this spring as a 50-FV prospect. Here’s part of what Eric Longenhagen wrote about him:

Horton’s delivery is fairly violent and indeed looks tough on his shoulder. Other aspects of his fastball are unexceptional, so it’s important for Horton to throw hard for that pitch to be effective. His secondary pitches are what drive his mid-rotation projection here. Horton’s slider and changeup both generate plus-plus rates of miss. His slider has rare velocity and two-plane tilt (it’s a weapon against both left- and right-handed hitters), and his screwball changeup gives him another way to get lefties out. Horton will probably work inefficiently as a starter unless his peak velocity returns, and will have to pitch off his secondary stuff a ton. He’s still likely to be an impact pitcher, but suddenly his list of career arm maladies has grown, forcing Horton toward the back of the overall Top 100.

So far at Triple-A Iowa, Horton has pitched to a 1.24 ERA and 3.58 FIP, with a 30.6% strikeout rate in 29 innings. His average four-seam velocity has climbed from 94.1 mph last year — when he made just nine starts at Double-A Tennessee and Iowa before being sidelined by a shoulder strain — to 95.8 mph thus far, a very promising development.

In isolation, the loss of Imanaga for a few weeks isn’t a serious problem for the Cubs, but the injuries are piling up. In mid-February, Assad strained his oblique; the 27-year-old righty made it as far as his second rehab start at Iowa before suffering a setback with the injury. The Cubs transferred him to the 60-day injured list to accommodate the addition of Flexen to the roster. But by far the bigger blow is the loss of Steele, which happened nearly a month ago but somehow never found its way into our coverage here at FanGraphs. After making his first All-Star team and finishing fifth in the NL Cy Young race in 2023 on the strength of a 3.06 ERA, 3.02 FIP, and 4.8 WAR, he was similarly effective last year (3.07 ERA, 3.23 FIP, 3.0 WAR) but limited to 24 starts due to a left hamstring strain and tendinitis in his left elbow. The 29-year-old southpaw was roughed up to the tune of a 6.89 ERA and 6.32 FIP in his first three starts of this season, but rebounded to throw seven innings in a combined shutout of the Rangers on April 4, allowing just three hits and two walks while striking out eight.

Unfortunately, before he could take his next turn, Steele told the Cubs he had experienced elbow tightness during that start. The team placed him on the 15-day IL with what was described as another bout of tendinitis. Counsell expressed hope that Steele would only miss the minimum, and the pitcher reportedly conveyed a similar expectation. Alas, a follow-up MRI revealed that he’d suffered a UCL injury, and on April 18, Steele underwent what the Cubs described as a “revision repair” of his UCL by Dr. Keith Meister. The terminology is getting murkier as variants of UCL repair procedures proliferate, but what that means is that this was not a full ligament reconstruction along the lines of Steele’s August 2017 Tommy John surgery, which he underwent while pitching for the Cubs’ High-A affiliate in his fourth professional season. “We’re looking at kind of about a year timeframe,” Counsell said afterward.

Thus a rotation that ranked 21st in our preseason Positional Power Rankings is now down the only two starters who projected to produce more than 1.7 WAR, and while the Cubs expect to get one of them back, that’s not a great place to be. The rest of the rotation has pitched reasonably well to this point, but it’s clear the Cubs are going to need to find some innings elsewhere, because with the exception of 33-year-old righty Jameson Taillon and 34-year-old righty Colin Rea, these starters have not shouldered substantial workloads in recent years. Taillon, a two-time Tommy John surgery recipient, has put up a solid but unspectacular 3.86 ERA and 4.09 FIP in 39 2/3 innings thus far. He’s developed into a dependable workhorse by post-pandemic standards, in that he’s one of just 15 pitchers who has reached the 140-inning mark in each of the past four seasons; he ranks 19th in the majors with 681 innings since the start of 2021 (including this season), though his 8.8 WAR in that span is tied for 52nd.

Matthew Boyd, whose two-year, $29 million deal made him the Cubs’ most prominent free agent addition this past offseason, has posted a 2.75 ERA and 3.74 FIP in 39 1/3 innings thus far. Even so, the 34-year-old lefty hasn’t thrown more than 78 2/3 innings in a season since 2019, with the pandemic, flexor tendon surgery in September 2021, and Tommy John surgery in June 2023 limiting him to a total of 263 innings from 2020–24. Ben Brown, a 25-year-old righty who debuted last season but didn’t pitch after June 8 because of a stress reaction in his neck, leads all Cubs starters with a 23.8% strikeout rate, but his 9.5% walk rate is tops among the group as well. Relying almost exclusively on a four-seam/knuckle curve combo, he’s generated a healthy 44.7% groundball rate, but has been touched up for a 4.88 ERA (though just a 3.72 FIP) across 31 1/3 innings.

Rea, a journeyman who set career highs with 167 innings and 0.9 WAR with the Brewers last year, has done an admirable job of filling in for Steele after beginning the year in the bullpen, where he threw 5 1/3 scoreless innings. When Steele went down, the Cubs were left to stretch Rea out on the fly, so he’s totaled just 24 2/3 innings in his five starts. In that time he has a 2.96 ERA and 3.12 FIP, and overall, he owns a 2.43 ERA and 2.98 FIP with a 20.3% strikeout rate. He’s using a different mix and different approach than he did last year with the Brewers, lowering his arm angle from 35 degrees to 30 and emphasizing his four-seamer, which relative to last year has increased from 93 mph to 93.9 and has gained a couple extra inches of arm-side run (from 6.5 to 8.5). He’s throwing the heater 52.7% of the time, up from 19.5% last year, with his sinker usage plummeting from 30.9% to 5.6%. Like Imanaga, he’s pitching up in the zone with the four-seamer with greater frequency than last year, but not to greater success, though overall batters have slugged just .361 against the pitch. In fact, Rea’s strong performance to this point has been driven by a newfound ability to avoid hard contact. He’s cut his barrel rate from 8.7% to 6.6% and his hard-hit rate from 42% to 38.4%; both of those represent improvements from percentiles somewhere in the 20s to percentiles somewhere in the 60s.

Presumably, if the Cubs continue to contend they’ll be in the market for a rotation upgrade prior to the July 31 trade deadline, though the ongoing buzz about their potentially targeting Marlins righty Sandy Alcantara has been tempered by the former Cy Young winner’s miserable return from Tommy John surgery; he’s been lit for an 8.42 ERA. Particularly while Imanaga recovers, the Cubs will have to cross their fingers and hope nothing else goes wrong in their rotation.