Archive for correlation

Long has the relationship between pitcher performance and batted ball metrics been dubious. The Sabermetric community has a solid understanding of why, fundamentally, a pitcher is good or bad. Strikeouts are good. Walks are bad. Hits by pitch are also bad. Home runs allowed are especially bad. So on, so forth. And by no means are batted ball metrics useless. It’s how we know ground balls allowed are superior to fly balls allowed, for example.

The community had hoped, however, that more granular batted ball metrics would help us better explain some of the more nuanced elements of pitcher performance, including those related to luck, such as batting average on balls in play (BABIP) and the percentage of home runs per fly ball (HR/FB). Since their introduction to the public sphere in 2015, and even with the inclusion of more granular Statcast data in 2016, any relationships that might exist between the physics and outcomes for batted balls during an individual pitcher’s season are still poorly explained. The following table depicts the correlations between pitcher BABIP and various batted ball metrics, sorted by the strength of the relationship (all qualified seasons, 2007-17, n = 898):

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More often than not, I write to hype a player who has wowed me in one way or another. Sometimes, I have to put a damper on things. Through 20 National Fantasy Baseball Championship (NFBC) drafts, Luke Weaver’s average draft position (ADP) stands at a pearly 111th overall and 28th among starting pitchers.

Weaver’s 36-inning debut freaked me out a bit. It was evident he could capably prevent baserunners, or, through 20% of a season, he could at least fake it. His 3.34 xFIP suggested as much, even in spite of his abhorrent 31% ground ball rate (GB%). Everything else stunk — all the luck metrics broke the wrong way in a small sample — but it was enough to suggest a bright future for the former 1st-rounder was imminent.

I planned to avoid Weaver at all costs in 2017 because of his fly ball tendencies exclusively; I simply did not want to suffer the wrath of a juiced ball because some small-sample strikeout-to-walk ratio (K/BB) goodness seduced me. Turns out, batted ball metrics can also feel the wrath of randomness in small samples, as his ground ball rate spiked to an above-average 50%. Some of the luck metrics tempered a bit, and the result was a 29% strikeout rate (K%) and defense-independent metrics that suggested he should nearly have a flat 3.00 ERA. It’s almost like there’s a reason why this 24-year-old kid was drafted in the 1st round or something.

I’m here to pump the brakes. I’m not sold on Weaver’s peripherals. I’m willing to let you convince me otherwise, but allow me to explain.

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I like a lot of pitchers who have unperformed this year. With strikeout and walk rates (K%, BB%) of 20.5 percent and 7.0 percent, respectively, Drew Hutchison delivers everything I want from a mid-rotation fantasy starter. With a 5.19 ERA and a 1.47 WHIP, however, he delivers a flaming bag of feces to my doorstep.

The same can be said for Taijuan Walker who, after a terribly rough start to the season, dazzled for seven straight starts before recently tossing three stinkers. With plate discipline ratios better than Hutchison’s and just 22 years old, Walker demonstrates the skill set and ceiling that have earned him consensus top-20 honors on prospect lists from 2012 through 2014. Yet his 5.06 ERA and 1.29 WHIP have left fantasy owners not only disappointed but also reeling.

Hutchison and Walker share a common trait: their ERAs dwarf their fielding independent pitching (FIP) statistics. FIP was designed to demonstrate a pitcher’s true performance in light of the events he can control — that is, events independent of balls put into play at the mercy of the defense supporting him (among other things).

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