The Correct Platoon Split to Use For Fantasy Baseball

June 24 3:37am

You’re setting up your FanDuel lineup. You’ve been watching the Rangers and you love the way Mitch Moreland is so solid in his approach at the plate. You’re giddy that he’s $1100 cheaper than the most expensive first baseman. Your finger is hovering over his name when you decide to check the opposing starter. Oh man, he’s a lefty.

You click over to Mitch Moreland’s player page and you find his platoon split and it’s ugly. So very ugly. A .544 OPS kind of ugly. A chill passes through you and you’re about to move on to another first baseman.

Should you?

Well, at first the answer is not as clear as Moreland’s OPS. First, you know sample size. You know his 90 plate appearances against lefties don’t provide a conclusive representation of his true talent level. A cursory check of one of the seminal pieces of baseball literature, Tom Tango’s The Book: Playing the Percentage in Baseball, and you find the relevant passage about platoon splits.

Reading it over, you learn that according to The Book, you are probably not looking at Moreland’s true talent versus left-handers until he’s taken 1000 plate appearances against lefties. Yeah, he’s a few short of that benchmark. In order to ‘make up’ for those missing plate appearances, you have to basically replace the missing 910 plate appearances with a league-average performance. For righties, the threshold jumps to 2200 plate appearances before you can truly ‘believe’ he’s bad against against left-handed pitchers.

Well, now you’re interested. You don’t want to bore yourself with the math, but you plow on ahead and do the regression. You take his observed platoon split, add in the league average platoon split, and divide it by the full 1000 plate appearances. Your rub your hands together, say a few chants, break a few pencil tips, and… yeah. He’s way closer to average, but you’re not looking for average. You’re looking for a no-brainer, great hitter in a great situation sort of thing.

You’re about to throw away the whole thing and take Mitch Moreland against Brett Anderson anyway. Brett Anderson is coming off the DL, and Moreland has two hits against him in five at-bats, so obviously he’s not terrible against all lefties. We can’t trust his career split against lefties anyway. Good idea, right?

Uh, not quite.

First off, there’s no reason to go the wrong way with your sample. Why take 90 plate appearances and turn it into five? That’s just not a good idea. You chide yourself, and your head hurts. You go get an adult soda to take the edge off.

Once you return to your desk with that fresh IPA, you’re about to move on from first base and take Moreland anyway, but something holds you back. If a small sample is bad, why not go for the biggest sample? How about the entire league over the past five years? How have lefties done against southpaws compared to right-handed pitchers over the past five years? Oh boy. Time for a hot pocket.

Three hot pockets later you’ve got it. Left-handed batters have shown an OPS of .701 against left-handed pitchers and an OPS of .776 against right-handed pitchers over the last five years. That’s more than ten percent better. It’s a good sample, too – over 200,000 plate appearances. So you’ve got a large sample, and though it’s not Moreland-specific, it does cover his upcoming game against Brett Anderson. And the common sense angle fits, too – managers bring in those LOOGYs (LeftyOneOutGuY) all the time to face lefties. Keep it simple, and keep the sample as large as possible.

Sigh. Time to find another first baseman for your FanDuel team. There’s got to be a lefty out there facing a bad righty. One more drink and you should be able to find him.

Eno Sarris will have a little fun on Fridays while using sabermetric research to try to help you better your FanDuel choices. He also writes for all three blogs at FanGraphs and recommends them heartily. In his free time, he does his best at Bloomberg Sports, RotoWorld, RotoHardball and the best Mets site out there, AmazinAvenue. He does what he wants to at and hopes you don’t mind.

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