● Obviously, we all know that batters typically do worse when facing a same-handed pitcher (e.g. a lefty batter facing a lefty pitcher). However, we can’t make any overarching statements about how much batters struggle against same-handed pitcher; the size of a lefty/righty platoon split varies from batter to batter.
● The same can be said for pitchers: while pitchers are normally better against same-handed batters, the size of a pitcher’s platoon split varies from pitcher to pitcher.
● Batters don’t have their platoon splits stabilize until at least 1,000 plate appearances against each hand (around 2,000 for right-handed batters), while pitchers have their platoon splits stabilize much faster (500-700 plate appearances against both hands).
Batted Ball Splits
● If a pitcher has an extreme batted ball profile – as in, they allow a high percentage of flyballs or groundballs – they will be more effective against batters that have a similar batted ball profile. In other words, if you put Tim Hudson (career 59% groundball rate) into a game against Johnny Gomes (career 51% flyball rate), I wouldn’t expect it to go well. Hudson would be more likely to succeed against someone like Derek Jeter, who has a career 57% groundball rate.
● Batted ball splits can have just as large an impact on a matchup as lefty-righty splits, but they don’t come into play as often because most hitters and pitchers have a neutral batted ball profile.
● Certain batted ball types are more likely to fall for hits than others. In 2010, line drives fell for hits 72% of the time, groundballs fell for hits 23% of the time, and flyballs went for hits 14% of the time. However, those percentages are based off BABIP, which excludes homeruns from its calculation; if you include homeruns, the flyball percentage bounces up to 21% of the time.
Pitch Type Splits
● There has been lots of work done over the last couple years to determine if certain pitches are more effective against same-hand or opposite-hand batters. The general rule of thumb is that pitches that move horizontally (e.g. sliders) work best against same-handed hitters, while pitches that move vertically (e.g. curves, changeups) are most effective against opposite-handed hitters.
● For a more complete list, here’s what I’ve been able to find over at Baseball Analysts and The Hardball Times:
Four-seam fastballs: Small platoon
Two-seam fastballs: Large platoon
Sinkers: Medium platoon
Sliders: Large platoon
Changeups: Small reverse-platoon
Curveballs: Small reverse-platoon
● In other words, pitchers should try and attack same-handed hitters with stuff like sliders, sinkers, and two-seam fastballs, while they should use changeups, curveballs, and cutters against opposite-handed batters. These are sweeping generalizations, though, and the optimal breakdown may vary depending on a pitcher’s movement and pitch repertoire.
● Small Sample Size - Whenever trying to draw a conclusion about a player’s talent, large samples are always better than small. See the Sample Size page for exact information on how large of a sample is good enough, but some statistics don’t provide predictive value even after a full season. And when you look at splits, you’re almost always looking at small samples. To avoid this, look at a player’s career splits and ignore anything with less than 500-1000 ABs.
● Regression to the Mean - Say a .350 wOBA player has a big lefty-righty split, something like .300 lefty wOBA / .360 righty wOBA. Going forward, should you expect their true talent level against lefties to be .300 wOBA or .350 wOBA? The correct answer is somewhere in the middle, depending how large a sample you’re using. If it’s a large sample (~1000 ABs versus lefties), you can expect their talent level to be somewhere in the .310-.320 wOBA range. If it’s a small sample, though, you have to expect that their talent level is closer to their career numbers than their split numbers, so maybe something in the .340-.350 range.
Links for Further Reading: