Collette Calls: The Dangers of Lefty Platoon Splits

This article is part of our Collette Calls series.

In April, I explained why I went after lefty-hitting outfielders. In short, I find them to be undervalued because they either struggle against lefty pitchers or their playing time is reduced because their managers do not allow the player to see the field when a southpaw is on the mound. You can accept the loss in playing time because it helps the player's batting average (and likely OBP) from tanking by being overexposed to their weakness. Sometimes, the manager alters those plans and lets the batter get more exposure to lefties if the hitter's defense is tough to take off the field or the hitter begins to show more success. A good example of this from this past season would be Josh Reddick.

The research from the FanGraphs library has this to say about splits:

You learn a lot more about a player in 400 PA than you do in 40. This is true over a full season or within a split. You need to pay attention to the sample size for each part of the split and not the overall sample size. A platoon split over 300 total PA won't tell you very much because you're likely only looking at 75-100 PA against lefties, which is simply not enough to tell you much about the hitter. You also have to be careful about using more and more seasons to increase your sample size because player talent changes and data from five years ago isn't as informative as data from this year.

In the case of Reddick, his performance against lefties had been worsening in recent years before this year's surprise turnaround. This whole scenario even played out in the World Series as Reddick was left in the lineup to face both lefty starters and even LOOGY's such as Tony Watson even though Cameron Maybin was waiting on the bench. Reddick's defense is so valued that A.J. Hinch left him in there, regardless of matchup, and he did not do very well this postseason because of it.

Using Reddick as our model, let's look at some of the other lefty hitters who did serious damage against lefty pitchers in 2017 to see if said player could be in for more playing time in 2018 or if this year was an aberration compared to earlier efforts. We'll begin with the lefty who led all lefties in batting average against fellow southpaws.

Gerardo Parra

Oddly enough, Choo's recent success against lefties is being offset by his struggles against right-handed pitching. Whereas he has made a career of raking righties, his numbers the last two seasons against righties are just .245/.341/.417. Frankly, it is tough to explain a lefty struggling this much against righties after doing so well throughout the rest of his career against them.

I would be remiss if I did not look into the other side of this coin – the lefties that lost all abilities to hit fellow lefties in 2017. No batter personified this struggle more than a Texas Ranger.

Rougned Odor

We have to be aware of platoon splits while not falling into the trap of recency bias. Hitters like Odor and Carpenter disappointed last year due to unforeseen struggles against lefties, but that should not deter you from rostering them in 2018. Conversely, hitters like Reddick, Dickerson, Choo and Parra may have a tough time repeating the success.