Pelfrey’s Splitter

Last night, Mike Pelfrey picked up his fifth win of the season, throwing seven and two thirds innings of two-run ball against Atlanta. Although Pelfrey is not as good as his traditional numbers suggest — those five wins and a 3.02 ERA — he has pitched slightly better this year than previously. His xFIP is 4.09 this year compared to a 4.60 career average. That change is largely the result of his increased strikeout rate: 6 K/9 this year, almost a full strikeout per nine more than his career average.

That could just be noise, but Pelfrey is doing things much differently this year. Previously he threw almost 80% fastballs (relying heavily on his sinker) and 13% sliders along with the occasional curve or change. This season he has dropped his fastball percentage down below 70% and has started throwing a splitter, doing so 17% of the time.

This shift is seen dramatically when he gets to two strikes. Before this year he still threw lots of fastballs in these counts, 76% of the time. Fastballs have, on average, the lowest whiff rate, so going with a fastball in a two-strike count is not the best way to get a strikeout. As a result most pitchers throw fewer fastballs in two-strike counts and instead go with breaking or off-speed pitches. Pelfrey’s two-strike fastball rate was quite high compared to average. This year in two-strike counts he has thrown just 62% fastballs, and goes with his new splitter 24% of the time. I think these two-strike splitters, which should lead to more whiffs than his fastballs, play a big role in his increased strikeout rate.

These splitters could also help Pelfrey against LHBs (against whom his career xFIP is an ugly 5.22). Sliders, previously Pelfrey’s main non-fastball pitch, generally have a large platoon split and are ineffective against opposite-handed batters. Splitters, like changeups, have little to no platoon splits, so the pitch could be an important tool for Pelfrey against LHBs.

At this point it is too soon to say that Pelfrey’s splitter will lead to an increased strikeout rate, smaller platoon split or, generally, make him a better pitcher. But the early indications are promising.




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Dave Allen's other baseball work can be found at Baseball Analysts.

15 Responses to “Pelfrey’s Splitter”

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  1. drbils says:

    Is there a rule of thumb for the point at which changes in pitch composition suggest that a pitcher is “not the same” as last year and should be considered to have a new “true talent” level (and expectations, etc.)? If pitch mix doesn’t do it, what about adding new pitches to the aresnal?

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  2. Patrick says:

    Pelfrey was throwing a curveball last night (in the mid 70s), something I haven’t seen before for him. Believe the story is he threw a curve in college, Peterson made him scrap it for a slider. FWIW.

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    • Gina says:

      Yeah he started throwing it again after Peterson was fired but it didn’t make much of a difference last year, the splitter has been the real change.

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  3. Franco says:

    I think the new Pelfrey is for real having seen most of his career starts. In the past, the difference between league average and replacement level Pelfrey has been his first pitch strikes since everyone could just sit on 4 seamers as soon as the count fell behind 2-0 2-1. When he got ahead of hitters, he was still pitching to contact. His splitter is more of a forkball in speed/movement which finally gives him an offspeed pitch to go with his 2/4 seamers. He’s probably not a 3 ERA type guy, but I wouldn’t be surprised to see him a legit #3 starter.

    His slider is awful and him not throwing it at all makes him a better pitcher.

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  4. BobLoblaw says:

    Strangely, his groundball rates haven’t changed with the addition of the splitter.

    Penny has also added* a splitter this year and instantly became a groundball pitcher.

    What’s the diff? Location? Break? Duncan?

    *or started using significantly more often than ever before

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    • Dave Allen says:

      I think the difference is in what the splitters were replacing. Most of Penny’s splitters came at the expense of fly-ball-inducing four-seam fastballs, while Pelfrey’s splitters came at the expense of his ground-ball-inducing two-seam fastball (his sinker). Fewer four-seam fastballs and more splitters = more ground balls. Fewer two-seam fastballs and more splitters = about the same maybe fewer ground balls.

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  5. Franco says:

    Yeah, the difference is Pelfrey would throw nothing but 2 seamers when he was ahead. Now he mixes it up with sinker and splitter when he’s ahead. The tradeoff is some more flyballs with some more swinging strike outs.

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  6. Matt S. says:

    Not to go overboard with the conspiracy theories, but I seem remember reading where Buck O’Neal believed that a “splitter” was really a “spitter” (I think it was in ‘the soul of baseball’, not sure). I bring it up because I have noticed Pelfrey is constantly licking his hand between pitches this year. Watch him, you will see. I don’t think he is only doing it when he throws the splitter because he does it between almost every pitch, but connecting that with O’Neal’s suspicion and his newly effective “splitter” makes me laugh. Is their more to this than meets the eye?

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  7. Franco says:

    Pelfrey got so bad with his mouth OCDs that he used to wear a mouth guard in 2009.

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