The Astros Don’t Need Lefties

Take a look at the Astros’ bullpen in the ALCS against the Yankees. Do you see anything odd about it? And no, this isn’t an article complaining about the fact that they rostered nine relievers in a seven-game series with multiple off days. Rather, it’s the fact that all nine relievers are right-handed that sets them apart from every other playoff team this season, and nearly every playoff team in recent memory:

This trend was largely true during the regular season as well. Despite leading the majors in bullpen ERA and FIP, just 48.1 of their 495.1 relief innings came from southpaws. Back in April, their Opening Day roster included 10 relievers, only one of whom, Blake Taylor, is a lefty. Taylor pitched just 19 innings with an average ERA, but walked more batters than he struck out. In June, he was placed on the IL with an elbow injury and pitched the rest of the season in Triple-A after he recovered. Aside from a cup of coffee from rookie Parker Mushinski, the remaining lefty innings came from deadline acquisition Will Smith, who posted a solid 3.27 ERA and 2.66 FIP in 22 innings down the stretch. But all three have been absent from their playoff rosters so far, with the Astros opting for right-handed pitchers instead.

This dearth of lefties clearly hasn’t inhibited the Astros’ success – through seven games, their bullpen has allowed just three runs in 33 innings, including a dozen scoreless frames to clinch their final victory of the ALDS. So how have the Astros dealt with their opponents’ left-handed hitters? For starters, it helps that no one they’ve had to face so far has been particularly vulnerable to lefties. Hitters in the opposing Division Series like Josh Naylor are great against righties and unplayable against lefties, but that hasn’t been the case with the Astros’ opponents so far:

While hitters like Rizzo and Carpenter don’t have career reverse splits like they did in 2022, they’ve only been marginally worse against left-handed pitching in their time in the big leagues. In other words, neither team had hitters that might inspire a manager to call on a lefty specialist. But the Astros’ effectiveness against lefties doesn’t just come from the tendencies of the hitters they’ve faced. Houston’s relievers are also well equipped to neutralize both left- and right-handed hitters. Consider the 2022 platoon splits of each reliever on the roster:

Seven of the nine righties in Houston’s bullpen actually fared better against lefties than righties in 2022, and the only one with a pronounced weakness against lefties – Martinez – has yet to appear in a postseason game. Lefties slashed just .207/.269/.341 against this group during the regular season, posting a .270 wOBA compared to the .284 wOBA right-handed hitters produced against them. Both of these numbers are significantly better than the league as a whole – across the majors, right-handed relievers allowed a .310 wOBA to lefties and a .307 wOBA to righties in 2022. But the fact that the Astros’ top five relievers by innings pitched all ran reverse splits during the regular season is particularly important, and shows the value in relievers who can deal with any type of hitter, especially in the era of the three-batter minimum.

Now, we know that reverse splits can sometimes be unreliable in a small, single-season sample. But in addition to the fact that four of these pitchers – Pressly, Montero, Urquidy, and Abreu – have career reverse splits over a multi-season stretch, it’s still valuable to consider the methods the Astros use to make their relievers so effective against potent lefties.

Much of the Astros’ success in opposite-handed matchups comes from their relievers changing their pitch mix depending on the handedness of the batter. One way that pitchers attempt to limit their platoon splits is by throwing multiple fastballs. Cutters and four-seam fastballs tend to be close to platoon-neutral, but the horizontal run of a sinker often directs the ball into the barrel of opposite-handed hitters, giving it one of the largest splits of any pitch type. Three members of the Astros’ bullpen – Montero, Neris, and Martinez – threw both a four-seamer and a sinker during the regular season. The trio combined to throw 582 sinkers, just 13 of which were thrown to a left-handed hitter. While many pitchers with multiple fastball types throw more sinkers to same-handed opponents, few take it to the extreme levels these Astros do.

Sinkers aren’t the only pitch types that can generate platoon splits, though. Sliders can generate splits just as large – we know that sweepers are ridiculously effective against same-handed hitters, but can be risky against opposite-handed hitters for the same reason sinkers are – with their horizontal movement moving towards the opponent’s barrel. Sharper sliders with more gyroscopic spin also run platoon splits, albeit less extreme ones. The Astros’ bullpen throws a variety of different slider shapes – Garcia and Martinez dominate the horizontal movement charts, while Stanek’s moves like a bullet, and others like Pressly and Abreu have a more hybrid shape, with high marks in both sweep and velocity.

All nine Astros relievers throw a slider, ranging in frequency from Neris’ 6.6% usage rate to Abreu’s 44% clip. Combined with a few of them also throwing sinkers, everyone in this bullpen has a clear plan to get righties out. But how can they succeed with a lefty in the box? Offspeed pitches tend to run the most neutral, or even reverse platoon splits, and it’s no surprise that the Astros selectively throw their offspeed selections to lefties. These offspeed pitches consist of splitters from Neris and Stanek — it’s each pitcher’s most-used secondary — and changeups from nearly everyone else. When looking at their offspeed and slider usage in tandem, we can see very stark differences based on the batter’s handedness:

In 2022, right-handed pitchers threw sliders to right-handed opponents about 28% of the time, as compared to just 13.6% for lefty hitters. In other words, righties roughly doubled their slider usage in situations with the platoon advantage. For changeups and splitters, there’s an even larger difference. Righty hurlers used their offspeed stuff 18.4% of the time against lefties, but largely shelved those offerings against righties, dropping their usage to just 6.9%. The Astros have taken this to the extreme, almost completely ignoring their unfavorable pitches in certain matchups. Montero, Neris, Stanek, Garcia, and Urquidy use their sliders as real weapons against righties, but throw them under 3% of the time against lefties. On the other hand, Montero, Martinez, and Garcia throw tons of slowballs to lefties but almost completely ignore them when their sinkers and sliders get the job done. Replacing sliders with changeups and vice versa is far from a novel concept, but the Astros’ optimization of their relievers’ pitch usage is on another level. Of course, it helps that they don’t have to face the order multiple times (unless they’re Luis Garcia), but they’ve still managed to collectively run reverse splits as a unit all season.

While Houston has good reason to put their trust in their righties, Smith is still waiting in the wings and should be available if the Astros want to add him to their World Series roster as a specialist. It’s pretty clear he shouldn’t face a string of righties – his .362 wOBA allowed to them matches the full season performance of Carlos Correa – but is there a use for him in a situation with two outs, a lefty up, and no great pinch-hitting options, possibly in the early innings? Smith had a very solid .278 wOBA allowed to lefties in the regular season, though that actually makes him worse than all of the Astros’ high-leverage arms, only besting lower-leverage relievers like Martinez, Garcia, and Urquidy.

Let’s consider Philadelphia’s roster for a second. Houston didn’t sweat the lack of left-handed relievers on the roster the past two series because the Yankees and Mariners didn’t have any lefties who were dangerous with the platoon advantage and pedestrian without it. What about the lefty hitters on the Phillies? In addition to measuring the magnitude of their platoon splits, we should also look at their ability to handle the pitches being thrown at them. Smith is a slider-heavy lefty, especially against fellow southpaws — he throws them about two-thirds of the time. If they decide to leave Smith off the roster and continue to lean on their righties, the Phillies will likely see a lot of changeups and splitters. Using Statcast’s run values, we can measure exactly how well each hitter performed against a given pitch type to see whether the Astros would rather go with Smith or a righty against any of these hitters:

Schwarber and Marsh had sizable splits during the regular season, and both find far more success against right-handed changeups than left-handed sliders. However, in late-game situations, the Phillies have right-handed outfielder Matt Vierling, who could hit should the Astros use a lefty. Vierling has started over Marsh against lefties, and has come in for Schwarber as a defensive substitute. The red-hot Harper has a platoon split of his own, but handles breaking pitches from lefties quite well, while Stott actually ran reverse splits during the regular season. With Vierling available off the bench and the three-batter minimum to contend with, it’s hard to see a case where Smith would clearly be better than someone on the current roster. However, three relievers – Garcia, Martinez, and Urquidy – didn’t appear in a single ALCS game. While Garcia and Urquidy are likely there to provide length and potentially an emergency start, Smith could replace Martinez as the ninth reliever in the unlikely event that his services are needed. I don’t think there has ever been a bullpen with six relievers that allowed wOBAs of .240 or lower against the batter handedness they should be weaker against, and the fact that we can’t find a clear and likely use case for a lefty specialist on such a large roster is a testament to this staff’s complete control over left-handed hitters. The Astros are four wins away from a World Series championship, and the fact that they’re dominant even in areas where teams aren’t meant to be is a huge reason why.