The Red Sox are struggling against left-handed pitching

A month ago, I was watching the Red Sox face the Angels in Anaheim on TV, and I found it curious that the Red Sox were starting Mitch Moreland against Tyler Skaggs. I found it surprising to start Moreland against the lefty because it was expected that Hanley Ramírez would get the bulk of the starts against left-handed starters. Hanley did DH, so it was not like he was missing out on crushing lefties. Andrew Benintendi was the odd man out that day, sitting in favor of J.D. Martínez in left field.

One could certainly make the argument that giving Benintendi a day off against a lefty makes sense. I would prefer playing him because he is not going to improve on his career line of .212/.309/.263 against left-handed pitching without getting further reps against them. But again, I understand the rationale, especially when the Sox were down one valuable right-handed batter in Xander Bogaerts.

The Red Sox booth understandably questioned manager Alex Cora’s decision to start Moreland against the lefty. They reported an unexpected answer from Cora. I’m paraphrasing, but they basically said that Cora stated that Moreland was starting because left-handed hitters have to be able to hit left-handed pitchers. He is not wrong, but the 32-year-old Moreland is pretty much a finished product. Benintendi is the one who is still developing.

The Red Sox increased aggression has benefited them

Photo by Sean M. Haffey/Getty Images

The increased aggressiveness of Red Sox hitters has been well documented. Let’s dive into that further and see how much is it helping them.

Of course, despite the fair concerns over starting Moreland against Skaggs, he still went 3-4 with a walk and a home run. Cora lucked out there!

Moreland is having a ridiculously good season so far, hitting .313/.395/.596 over 114 PA. His 163 wRC+ is tied for ninth in all of baseball among hitters with at least 110 PA. Considering that he has never had higher than a 117 wRC+ in a season, he is sure to come back down to earth. He has a .347 BABIP, and his batted-ball profile is roughly in line with his track record. He is walking quite a bit more, and he is being more aggressive on pitches in the zone, which is a team trend, but none of that goes far enough to explain a .418 wOBA that is 90 points higher than his career wOBA.

The Red Sox currently have one of the worst performances against left-handed pitching in the majors. That might come as a surprise for a team that has Bogaerts, Martínez, Hanley, and Mookie Betts, but the team’s .299 wOBA against LHP ranks just 25th in the majors. Outside of those four lefty mashers, the Red Sox are left with left-handed hitters and struggling right-handed hitters.

A week or two ago I was watching another Red Sox game, and one of the members of Boston’s booth that day suggested that Moreland start more often against left-handed starters over some of the struggling right-handed hitters on the team. Their reasoning consisted of citing Moreland’s success against lefties this season.

I imagine many had the same reaction as I did when hearing that. I rolled my eyes.

Moreland is indeed hitting well against lefties so far this season, slashing .273/.360/.455, good for a .356 wOBA. But as I have discussed in the past, even an entire season of platoon splits are a small sample size. Moreland’s twenty five plate appearances this season against southpaws is basically nothing. His .299 wOBA over 758 career plate appearances versus left-handed pitching is obviously much more meaningful, but even that is not enough plate appearances to measure left-handed hitters’ true talent splits.

Moreland’s career splits need to be regressed to the mean. Research done in the sabermetric tome The Book details how to do this, and Matt Klassen wrote a good primer on the subject at FanGraphs.

I bring this up because I was curious to test the Red Sox booth’s suggestion about Moreland. They do have some bad right-handed hitters, after all, such as Christian Vázquez and Eduardo Núñez. The only proper way to test this is to determine the players’ true talent against left-handed pitching.

I crunched the numbers for this exercise using this calculator make by Ian Malinowski of DRays Bay. It probably needs some updates, but it should serve for what I am trying to accomplish here. The projections were taken from ZiPS. I also wanted to compare Moreland to other left-handed hitters, so they are included here as well. I left out Bogaerts, Martínez, Hanley, and Betts for obvious reasons.

Moreland is indeed better against lefties than Vázquez, but obviously those broadcasters did not mean that Moreland should play catcher sometimes. I thought perhaps Núñez would be worse, as he strangely has reverse splits for his career. However, it regressed to a .309 wOBA which is just two points higher than his projected wOBA versus righties. So as expected, Moreland should not be starting over any right-handed hitters unless he learns to catch.

It is probably not too surprising that Moreland’s true talent against lefties is inferior to that of Brock Holt and Rafael Devers, despite the latter’s current struggles this season. I did find it interesting that Benintendi and Jackie Bradley Jr. did not fare so well.

Benintendi is just several weeks shy of 24 and is only in his second full season in the majors. Some growing pains are to be expected. He is talented and still developing. There is no reason to believe he will not improve as long he continues to get plate appearances versus left-handed pitching. He has appeared in 22 games against them so far this year, so thankfully he is not getting the Michael Conforto treatment.

JBJ, however, is the bigger problem. He has not hit well since 2016, and this year he is hitting a paltry .165/.267/.252. Even with his excellent center field defense he is going to struggle to crack replacement level with a 44 wRC+. Moreover, he is 28 years-old and has shown a serious decline in offensive skills since last season. The evidence points towards Moreland as the better option versus left-handed pitching.

Given everything spelled out here, it would make the most sense to sit Bradley more often against lefties in favor of Moreland. Hanley can DH, Benintendi can move to center, and J.D. can spot start in left field. Moreland is also a better fielder than Hanley, but the outfield defense would be weakened. I believe that the offensive gain would be substantial enough to make it worthwhile.

The Red Sox have a great analytics department, and Cora has shown himself to be amenable to analytics. It will be interesting to see how the team addresses its struggles against left-handed pitching going forward.