I don't think anyone could have missed the fuss over pitchers' claims that the World Series baseballs are unusually slick, and it's affecting their sliders by reducing the pitches' movement. I have no real opinion one way or the other, but I did take issue with the claim that PITCHf/x data clearly show this. While arguing with one dude on Reddit, I made the following: These are Verlander and Kershaw's sliders, game by game, regular season plus World Series, showing the distribution of horizontal and vertical movement. Only I randomized the order of the games, and I challenged the dude on Reddit to pick out the World Series games from this set. (He hasn't done it yet.) The correctly ordered versions, labeled by date, and also including Darvish, Giles, Keuchel, Peacock, and Giles, are here (if I'm doing this right). I genuinely don't have an opinion on whether the balls are changed, though I'm moderately skeptical. I don't see a consistent, believable effect from PITCHf/x, but I don't discount the comments from a half-dozen people who are among the world's experts on how a baseball should feel.