The Postseason’s Quieter Pitching Revolution

“More breaking balls!” That’s how Theo Epstein characterized the postseason for Brian Kenny on the latter’s lead-in show before Game Five of the World Series. It’s a notable observation insofar as it’s a little more actual content than you typically get publicly from a high-ranking front-office exec, but it’s also a matter of public record that his team was seeing a ton of breaking balls in the World Series. Dave Cameron, for example, took an excellent look at the subject earlier this week.

What’s interesting about Epstein’s comment, however, is how he was somehow able to remain vague about his point, even as he seemed to be offering something incredibly specific. He suggests there are more breaking balls in the playoffs, sure. But it’s not clear if he’s implying that there are more breaking balls every postseason for every team, or merely that there were more this postseason for his team, or something in between.

This postseason was defined by a transformation in bullpen usage; that’s not up for discussion, really. But it seems possible that pitching mixes themselves also changed this postseason. And while it would be impossible for Andrew Miller to throw 225 innings and strike out nearly 400 batters — the unfathomable numbers you get if you prorate his postseason work to a full season out of the pen — it might be possible for starting pitchers to throw more breaking balls all season. This postseason trend (if it actually exists) could inform the regular season in a real way.

At first blush, there actually appears to be no postseason preference for the breaking ball. Perhaps this is because starting pitchers find an extra half-tick on their fastball in October, and they like throwing their harder fastballs.

Both the four- and two-seam rates increase, which suggests that there aren’t universally more breaking balls in the postseason.

But let’s see if something has changed more recently by breaking up the playoff years into their own rows.

Organized this way, it seems like batters are seeing more sliders generally, and more curves this season. It’s tempting to conclude that we’ve found it. More curves for everyone! Baseball is changing.

Back to Cameron’s piece, though. He found that the Cubs saw way more breaking balls in the World Series — and that it was perhaps due to advanced scouting reports identifying a teamwide weakness against the curve. Indeed, the Cubs played more games than almost every other club this postseason — a full 23% of the postseason pitches you see above were thrown to Cubs batters. So, let’s replace the Cubs with a league-average line in this year’s postseason numbers and see what it looks like after that adjustment.

So, okay. There appears to be a bit of a trend here beyond just what the Cubs themselves experienced. Two-seamers are mostly thrown for contact, to get a ground ball, so maybe it makes sense to replace a few sinkers with curves when the game is on the line. This also makes sense in the context of our obsession with spin rates right now: the benefit of spin is easiest to decipher when it comes to four-seamers and curves, after all.

We saw pitchers like Rich Hill and Drew Pomeranz push their curveball rates up to about 40% this season. The combination of spins on their four-seamers and curves work so well together that neither of them require a large arsenal. Could we be seeing the dawning of the age of the yakker? Are curveballs slowly becoming more popular, but we’re just noticing it now because we just finished watching the only baseball game on television together every night?

Perhaps. Let’s look at the regular-season trends again — in this case, with a slight adjustment. Our leaderboards classify knuckle curves and curves as different pitches, so I combined a few pitch types to get a better sense of larger pitch-type trends.

Maybe there is something here. In raw terms, we saw 5,398 more curveballs this past season than we had ever seen previously in a season in the PITCHf/x era. Among starters, the effect is magnified: curveball percentage increased from 9.9% in 2010 to 12.0% this past season. Every pitcher is becoming more like Rich Hill, maybe.

A side note: while it might be true that curves are more prevalent in the game today, it’s not clear that the pitch is being used differently. Despite the anecdotal evidence that pitchers like Hill are able to coax more swings on their curves due to the deceptive spin, the swing rate on the curveball is steady (40.5% this past season, 40.2% since 2007). And though Hill throws the ball in the zone a lot, the curve in general hasn’t become fastball-like in terms of zone rate (31.3% zone rate this past season, 33.3% since 2007).

Maybe, instead, teams have just decided that heavy curve usage isn’t as dangerous as we once thought. Predicting pitcher injury is such a difficult task, maybe more teams are throwing up their hands and saying, “Sure, throw the curveball 30% of the time. Why not? It’s a pretty good pitch.”