Expected Platoon Splits
A couple of weeks ago, MGL formulated a regression equation that estimated platoon splits based on different pitch types. Max Marchi has found the average run values for different pitch types by batter handedness as well. I ran my own regression equation using pitch velocity and movement to find an expected value of pitches against batters of different handedness.
Pitchers are often placed in the bullpen if they prove incapable of getting opposite-handed batters out. In relief, the ability to get same-handed batters out can be leveraged. In fact, the majority of players with large expected platoon splits are relievers.
Mike Macdougal, a sinker/slider pitcher with a tailing sinker and a sweeping slider has the largest expected platoon split in my sample. As for left-handed pitchers, I was very surprised to learn that Daniel Ray Herrera has a strong platoon split. The changeup is the great neutralizer when it comes to the platoon advantage, and I've always thought of the screwball as a mutant changeup in that it also moves toward same-handed batters. But Herrera is useless against righties. That Herrera has a high LOOGY score is just another mark in his favor for sabermetric fans. I hope by now we all know about the joy of his screwball. But even when he was in college, one stat-savvy fan wrote a ballad for Herrera, and Herrera has since become the mascot for collegesplits.com* Similarly, Hideki Okajima, whose over-the-top delivery I would think allows same-handed hitters to see the ball out of his hand, actually has much greater success against lefties than righties.
*I like to think of Yankee farmhand Pat Venditte as the current Herrera. Seen as trick-pitchers by scouts (Herrera because of his screwball, Venditte because he's a switch-pitcher), both Herrera and Venditte have encountered nothing but success. Venditte has been putting up better numbers in the Minors than he did as a walk-on-turned-All-American at Creighton. At 25 years old, Venditte has thrown 36 innings in High-A this year, striking out 48, walking 9, and allowing one homer. People say that his gimmick won't work when he has to face Major League hitters, but I say the game's the same, just gets more fierce. I fear that the only reason the Yankees have yet to promote him is that they don't want to disrupt the structure of every baseball database in the world, as pitcher-handedness has never been tracked by at-bat. Anyway, if I had to guess, I'd think Venditte would perform better as a southpaw, given that he has subpar stuff from both sides, yet he still tries to get it done conventionally as a righty. His sidearm approach as a lefty could at least give Major Leaguers a different look.
Sinkerballer Fausto Carmona has the largest expected platoon split for a starter. He's struck out as many lefties as he's walked in his career, but for some reason he's found more success as a starter than he did in the bullpen, where he had one of the most disastrous runs as a closer of all-time. Carmona's former battery-mate CC Sabathia is also Carmona's counterpart when it comes to left-handed starters expected platoon splits. However, Sabathia is fine against righties, and otherworldly against lefties, which is why he's never been considered as a reliever.
I think J.A. Happ would have the most to gain of any starter by being placed in the bullpen, in spite of his quality changeup. Dontrelle Willis, too. Why hasn't he been tried in the bullpen? Junkballer Matthew Mahoney has one of the few expected reverse platoon splits, although that hasn't come to fruition in his time in the Majors. Chris Tillman, too, has an expected reverse platoon split, so I think it's wise that the Orioles break him in as a starter and keep him in the rotation if only at AAA. And Jennry Mejia's cutter, like Mariano Rivera's, should be either \as good or better against lefties as it is to righties, so that's another reason he should be given every attempt to start. It's Oliver Perez who might be better suited for the bullpen, as he would have utility as a LOOGY.
Joe Maddon and the Rays have surrendered the platoon advantage against changeup specialists a couple times this year. Maddon has stacked the lineup with same-handed batters against such pitchers, and even ordered switch-hitters to bat from their unnatural side. The switch-hitter thing is just crazy, but maybe there's something to a reverse platoon splits with changeup guys. The Rays' front office is known for going the extra 2%, which includes PITCHf/x analysis. But if the decision is coming from any higher up than Maddon, I don't know what data they're looking at. (If Maddon is making the decision, it's off of splits from this year and whatever biases come from being no-hit twice by chaneup artists.) RHP Shaun Marcum and LHP John Danks have been better against opposite-handed batters than same-handed batters, but I don't see anything in their PITCHf/x profile that would suggest their projected platoon splits should be so far from the mean. It's much easier to say which pitchers' reverse platoon splits are fake (I'd say a couple of Giants in Jeremy Affeldt and Sergio Romo) than whose are real.
In doing this analysis, the pitcher in whom I was most interested was Justin Masterson. Ever since he broke into the Bigs, the word was that his sidearm delivery was more suited for relief than starting. His performance has been acceptable as a starter, but his enormous platoon split has reinforced the notion in some minds that he should start. I didn't include him in my sample, since he's a sidearmer, but I predicted his out-of-sample performance anyway. His slider is a fine pitch to both RHBs and LHBs. To righties, both of his fastballs are truly unique pitches, and have been hugely successful. The problem is that his sinker is his best pitch, and he chooses not to throw it to lefties. And his four-seam fastball is rendered ineffective against LHBs, so he's handcuffed himself to only his breaking ball. Without another offering, I don't think he'll ever be able to get lefties out.