What changed? Why trust your lefty masher against some righties but not others?

The answer has less to do with Hernandez than with the starters. For whatever reason, McCullers and Morton both elicit reverse platoon splits, which means they have better success against left-handed hitters even though they, themselves, are right-handed. Pitchers with reverse splits are exceedingly scarce in today’s ultra-specialized game, and it’s particularly rare to have two statistical oddballs in the same playoff rotation.

That said, McCullers and Morton aren’t the only ones. Recently, we took a look at the hitters with reverse splits at the plate. Now it’s time to examine the starting pitchers that do, an eclectic group headlined by two Astros.

McCullers, RHP, Astros
2017

McCullers’ reverse platoon splits are somewhat unexpected, given that his changeup, which would run away from lefties, is his third — and probably least effective — pitch. It’s usually pitchers with poor changeups who struggle against opposite-handed hitters, but not McCullers. McCullers relies heavily on his knuckle curve, which, in theory, should break down and into the swing of a left-handed hitter. Despite all that, righties hit him much better (.264/.346/.419) than lefties did (.231/.294/.312). Three of four extra-base hits McCullers allowed in the postseason came against righties.

Career
McCullers allows 109 extra points of OPS to righties (.253/.341/.403 career) than lefties (.232/.299/.336) over the course of his three-year career. The 107-point platoon difference in OPS he allowed last season was McCullers’ starkest, most extreme split yet. Interestingly enough, McCullers’ father, Lance McCullers Sr., also pitched to reverse splits over his seven-year career.

What does Statcast™ say?
In this section, we’ll turn to Statcast™ to tell us what these pitchers’ peripherals say about their reverse platoon splits. We’ll look at the Statcast™ metrics expected batting average (xBA), expected weighted on-base average (xwOBA) and barrels, which use exit velocity and launch angle data to describe quality of contact and tell a larger story about the things pitchers can control.

By percentage, no right-handed starters threw more breaking balls to lefties than McCullers, who threw more half of his pitches to lefties with spin. That helped McCullers rank in the top 10 in xBA (.224) and xwOBA (.276) vs. lefties. McCullers’ xBA against was nearly the same against righties (.225) and lefties (.224), though, implying he outperformed expectations against righties.

Morton, RHP, Astros
2017

No qualifying right-handed starter held lefties to a lower batting average against (.175) or opponent slugging percentage (.298) than Morton, the Astros’ breakout star of the postseason. Against lefties, his strikeout-to-walk ratio leaped from 2.65 to 3.92. Morton struck out 25 more lefties in 43 fewer chances.

Career
Morton has reinvented himself multiple times over the course of his 10-year career, so his overall line isn’t completely reflective of the pitcher he is today. That said, 2017 was the first year since ’14 that Morton showed reverse splits, and third since 2012.

What does Statcast™ say?
Morton slightly outperformed his .204 xBA and .273 xwOBA against lefties, which ranked third and fifth among qualifying right-handed starters. He allowed just six barrels to lefties all season, posting a 0.25 barrel-per-pitch percentage (third lowest) and 1.2 barrel-per-swing percentage (fifth lowest) against them that ranked well among qualifying right-handed starters.

Morton's first K of the game

Stephen Strasburg, RHP, Nationals
2017

Last season was arguably a career year for Strasburg by many measures, and his success came during a season over which he used his changeup as often and more effectively than ever. Strasburg’s hard change is a weapon against left-handed hitters, darting down and away from them. That could help explain his career-best success against lefties, whom he held to a combined .193/.265/.324 slash line. Righties didn’t fare much better, but did find marginally more success in their .215/.265/.324 line.

Career
Strasburg’s reverse splits began to emerge midway through his career, when he started incorporating the changeup more fully into his repertoire. Since then, his success against lefties has been constant enough to override some lumps he took against them as a young pitcher in his overall career line, which now looks fairly even platoon-wise. But over the past five years, Strasburg had fared much better against left-handed hitters, holding them to a combined 267 fewer points of OPS compared to righties.

What does Statcast™ say?
Strasburg held lefties to a .195 xBA last season, the lowest among qualifying right-handed starters. That number also easily beat out the .208 mark righties posted against him. Strasburg held lefties to a .261 xwOBA, second best among full-time right-handed starters and slightly lower than the .267 mark he allowed to righties. He also threw significantly more changeups (21.4 percent of his pitches) to lefties than he did to righties (15.7 percent).

Strasburg K's his sixth in a row

Greinke, RHP, D-backs
2017

The D-backs’ ace actually faced more lefties than righties this season. They sacrificed 39 points of OPS against him, hitting .241/.284/.373. Righties hit .217/.260/.402.

Career
Greinke is more a master craftsman now than the power arm he was earlier in his career, so it wouldn’t make a ton of sense to look at his total career line, which looks more typical of a right-handed starter split-wise. But he’s been better against lefties in three of the past four seasons, meaning the 2017 numbers are part of a trend, not an abnormal blip.

What does Statcast™ say?
Greinke was excellent against all hitters in 2017, but Statcast™ disagrees somewhat with his reverse splits. Lefties made better contact (.226 xBA, .288 xwOBA) than righties (.209 xBA, .274 xwOBA) against him, though those numbers still rank among the lowest in baseball.

Rich Hill, LHP, Dodgers
2017
Because of his wacky arm angles and relentless breaking ball use, conventional thinking would pin Hill as a lefty designed to dominate left-handed hitters. Heck, he’s spent parts of his career as a lefty specialist.

But Hill was significantly better against righties last season, holding them to a .190/.252/.331 line. Lefties enjoyed 262 more points of OPS, hitting .255/.407/.439 against Hill.

Career
Hill’s overall career splits are conspicuously even, but he’s pitched in a variety of roles and styles over parts of 13 seasons. Since he returned as a full-time starter in 2016, his reverse splits are consistent and stark.

What does Statcast™ say?
No left-handed starter held righties to a lower xBA (.182) than Hill, whose .250 xwOBA against righties ranked third among lefty starters (behind Chris Sale and Clayton Kershaw). Hill underperformed his quality of contact numbers slightly against lefties (.224 xBA) and outperformed them slightly against righties (.182 xBA), meaning the reverse splits are real, though slightly exaggerated.

Hill strikes out Springer

Other notable starting pitchers with reverse splits: LHP Hector Santiago (Twins), LHP Eduardo Rodriguez (Red Sox), RHP Sonny Gray (Yankees), RHP R.A. Dickey (free agent), LHP Matt Moore (Giants), RHP Chase Anderson (Brewers), RHP Marco Estrada (Blue Jays), LHP Jason Vargas (free agent).

Joe Trezza is a reporter for MLB.com based in New York. Follow him on Twitter at @joetrezz. This story was not subject to the approval of Major League Baseball or its clubs.



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