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How an Underrated Prospect Became a Star and Nearly Single-Handedly Fueled the Cardinals’ Playoff Run

Right-hander Jack Flaherty is in the midst of a historic stretch since the All-Star break, shutting out opponents and helping St. Louis push to end its postseason drought

Getty Images/Ringer illustration

Among the 10 teams currently in playoff position, the Cardinals have had the fewest star-level seasons. Literally so, using 2019 All-Star selections as the heuristic; shortstop Paul DeJong was St. Louis’s lone representative at July’s exhibition.

The other teams with just a single player were the Blue Jays, Orioles, Royals, Tigers, Mariners, Marlins, Phillies, Giants, and Padres—all will likely miss the postseason, with all but the Phillies stumbling to well-below-.500 records. But the Cardinals, unique among playoff teams, have succeeded despite a general lack of standout performers. Even DeJong has cooled since a hot April, and now totes a batting line only slightly better than average.

In part, this mundanity fit the Cardinals’ broader team situation at the midseason break: They were definitionally average, in third place with a 44-44 record and almost exactly as many runs scored as allowed. They were stuck in the same sort of rut in which the past three Cardinals teams had spun their wheels aimlessly: not so poor as to inspire a teardown, nor so ambitious as to compete with the Brewers or Cubs atop the division.

In the other part, the reason the Cardinals didn’t have more All-Stars was because their best players weren’t performing like they deserved that designation. Even now, as the regular season approaches its end, Paul Goldschmidt has never hit this poorly over a full season. The same goes for Matt Carpenter. Yadier Molina and Harrison Bader have been below average at the plate. Opening Day starter Miles Mikolas has a 100 ERA+, meaning he’s been exactly average. Closer Jordan Hicks had Tommy John surgery, and setup man Andrew Miller is suffering through his worst season as a reliever.

And yet, two months after the All-Star Game, the Cardinals are in command in the NL Central, with a four-game lead over the Cubs and, according to FanGraphs, a 77.4 percent chance to claim the club’s first division title since 2015. Only the Astros have a better record in the second half than the 37-19 Cardinals, who have found not just a new, compelling star, but a pitcher in the midst of a historic second-half run. Jack Flaherty is almost single-handedly propelling St. Louis to the playoffs.

The notion of a solo effort on a roster with dozens of players is almost always an exaggeration, but in Flaherty’s case, it comes close to the truth. In the second half alone, Flaherty has been worth 3.0 wins above replacement—second among all pitchers to Justin Verlander’s 3.6—which by itself accounts for nearly all of the separation between the Cardinals and Cubs. A closer look at Flaherty’s game-by-game results reveals the extent of his recent dominance.

In his most recent start, the 23-year-old right-hander shut out the Pirates over eight innings, striking out 10. In his last start before that, he shut out the Giants over eight innings, allowing just one hit. And those gems might not even represent his most impressive showings of late: He twirled seven shutout innings against the Dodgers, and before that allowed just one hit over seven shutout innings against the Cubs, and before that held the Astros’ version of the Murderers’ Row to just two runs in a win that thrust the Cardinals into sole possession of first place.

Overall, in 11 starts since the break, Flaherty has allowed zero runs seven times, en route to a 0.76 ERA. If his second half ended today, that would be the second-best split performance since the deadball era.

Best Split-Half Performances by ERA, 1920-2019 (Min. 10 Starts)

Pitcher Season Half ERA
Pitcher Season Half ERA
Jake Arrieta 2015 Second 0.75
Jack Flaherty 2019 Second 0.76
Stephen Strasburg 2017 Second 0.86
Kris Medlen 2012 Second 0.94
Roger Clemens 1990 Second 0.97

Flaherty has also allowed a .151/.220/.229 slash line in the second half, essentially turning all opposing hitters into Jeff Mathis. Batters’ OPS+ against him since the break is 19, meaning that after adjustments for ballpark and league context, he has allowed an OPS 81 percent lower than average. That mark also places him in rarefied territory. (And no, this chart is not mistaken: In 2000, Pedro Martínez really did post two of the top eight pitching halves in the past century, by adjusted opponents’ OPS. The more amazing part is that he might have been even better the previous season.)

Best Split-Half Performances by OPS+, 1920-2019 (Min. 10 Starts)

Pitcher Season Half OPS+
Pitcher Season Half OPS+
Jake Arrieta 2015 Second 13
Clayton Kershaw 2015 Second 16
Johan Santana 2004 Second 18
Pedro Martínez 2000 Second 19
Jack Flaherty 2019 Second 19
Pedro Martínez 2000 First 24
Stephen Strasburg 2017 Second 24
Greg Maddux 1995 First 25

Acknowledging that it’s impossible to expect any pitcher to put forth numbers like these, it’s remarkable that Flaherty of all pitchers would be in this position. At Harvard-Westlake in Los Angeles, Flaherty was the third-best pitcher on his high school team; he watched MLB clubs select older teammates Max Fried (seventh) and Lucas Giolito (16th) in the first round of the 2012 draft before going 34th overall to St. Louis in 2014.

Even then, as a sandwich-round pick who threw well enough in the minors to place on top-100 lists, Flaherty didn’t dazzle or hint at future acehood like Giolito. For instance, a clear trend emerged in his writeups in the annual Baseball Prospectus guidebook. In four consecutive preseasons from 2015 to 2018, BP used the term “mid-rotation” to describe his future, in one year noting that compared to his high school teammates, he “doesn’t come equipped with their ceilings.” Highlighting that assessment isn’t a slight against BP; no prospect site thought he would mature into anything more than a no. 3 or 4 starter. But in the same year that Giolito and Fried have surged at the MLB level, so too has Flaherty.

The Cardinal’s future looked rosier after last season, when 151 innings of 3.34 ERA pitching earned him a couple of down-ballot Rookie of the Year votes, but a sophomore slump hit Flaherty hard in the first half of the season. As late as July 2, his ERA was 4.90, with relatively poor peripherals to match. His second half has looked superior to the first in every conceivable statistic.

Jack Flaherty’s 2019 Splits

Statistic First Half Second Half
Statistic First Half Second Half
Games 18 11
IP/Game 5.4 6.5
ERA 4.64 0.76
FIP 4.74 2.19
Slash Line .237/.300/.444 .151/.220/.229
HR Allowed 20 3
K% 26.4 33.2
BB% 7.9 6.3

It’s difficult to detect any meaningful change in Flaherty’s approach that might explain this disparity. He’s used his four-seamer and changeup a bit less, his two-seamer and slider a bit more, but not tremendously so. Neither do his pitch locations look all that different, or are his pitch velocities or movement profiles changed. He just seems to be executing his pitches better, in particular avoiding the hard contact that—in the highest-homer season in MLB history—ruined so many starts in the first half.

He’s also benefited from substantial luck. In the second half, Flaherty has allowed a mere .221 BABIP (third lowest among qualified pitchers), stranded a league-high 94.9 percent of baserunners, and allowed a league-low homer-per-fly-ball rate of 4.8 percent. None of those figures should be remotely sustainable over a full season, even if Flaherty allows plenty of soft contact and the Cardinals’ sturdy defense helps turn those flares and dribblers into outs.

Yet of course Flaherty has been lucky. It’s impossible to post an ERA figure that starts with a zero for any stretch of time without ample fortune; Strasburg’s dazzling second half in 2017 stemmed in part from a league-best HR/FB rate, and during Arrieta’s second half in 2015, which won the Cubs righty a Cy Young award in an outrageously competitive race, he ranked second in BABIP, first in strand rate, and second in HR/FB rate.

That Flaherty’s run is predicated in part on a set of unsustainable indicators raises natural questions about regression, but just because Flaherty will regress at some point doesn’t mean he has to do so before this season ends. His homers and such might not tick back up until 2020. Strasburg in 2017, for instance, continued his torrid pace with 14 shutout innings across two playoff starts, and Arrieta began his 2015 postseason with a complete-game shutout against Pittsburgh in the wild-card round.

There’s some reason for concern beyond this season, but the Cardinals and their fans, in this moment, shouldn’t care. Not when the Cardinals are three weeks away from ending their longest playoff drought in two decades. Not when Flaherty has already blown past any realistic projection of him as a prospect, to the point where he has a real chance to end up with the most strikeouts in a single season for a St. Louis pitcher since Bob Gibson. And not when, again, he has allowed zero runs in a majority of his starts since the All-Star break, putting a team that needs wins into a winning position basically every time he takes the mound.