The Good News About Corey Kluber on Short Rest

By the time a pitcher gets to October, his body and his mind are headed in different directions. The head can’t stop racing, but the body is battered by six months’ worth of battle. That probably seems intuitive, but it’s actually relevant tonight in a very concrete way: Cleveland right-hander Corey Kluber is once again going to climb the mound on short rest, with body and mind at odds. Here’s the good news for Indians fans, though: while the results of postseason short-rest starts isn’t great, the process — which is to say, the movement and velocity recorded on pitches — suggests that adrenaline trumps all when it comes to postseason ball.

First, we should update Jeff Sullivan’s excellent piece on short rest from 2013, especially since we’ve had 15 short-rest starts in the playoff since then. Here are the short-rest starters put up against the regular- or plus-rest starters in a few results-oriented categories.

By results, it still appears as though short rest renders a pitcher a lesser version of himself. And that makes sense, because pitchers have routines based on the five-man rotation. Taking a day of rest away upsets that routine, while also of course taking a day of rest away.

But if you look at this table against the old one, you’ll see that the gap between the two groups has closed. That could be because I used pitchers since 2007 instead of going all the way back, sure, but it’s also interesting that the subject of that piece — Clayton Kershaw — has continued to pitch on short rest since Sullivan published his piece and has garnered his team two postseason wins in the process. Maybe clubs have gotten better at picking who will start on short rest since short-rest appearances peaked in 2003 with 16.

Process is the key word here, though. With the existence of PITCHf/x and Statcast, it’s possible to look at stuff now in a way that wasn’t previously. Comparing the movement and velocity produced by starters on short rest in the postseason to the movement and velocity of those same pitchers, on regular rest, in the regular season, allows us to learn more about the stuff pitchers have exhibited on short rest. That’s good news because 128 short-rest starts scattered among so many pitchers still feels like a short sample.

First, let’s look at velocity.

Short rest has almost no effect on velocity. The data here is entered manually from Brooks Baseball. Brooks measures velocity from a different starting point than the data that appears at FanGraphs, so you can mentally subtract a mile per hour from all of the numbers if you want. They’d still all look the same relative to each other, though — which is to say, they’d feature a slightly higher figure for the postseason short-rest group.

As for that slightly higher figure, be careful: you don’t want to say that pitchers throw harder on short rest. I found that starters got about a half mile per hour of extra velocity in the 2015 postseason — the postseason bump. So you see the adrenaline bump here, not a short-rest bump.

The point is that there’s little difference. And that follows when it comes to movement. Check out the average vertical movement on the short-rest pitches versus the same group in the regular season.

In each case, the short-rest situation has ended up producing better vertical movement for the pitcher. He’s had more ride on his four-seam, more sink on his sinker, more drop on his breaking balls and changeups. Given that the player most sampled here is Kershaw himself, with five postseason starts, the sample isn’t huge. Maybe pitchers finish their pitches better in the postseason, even on short rest. What it more likely demonstrates, though, is that short rest doesn’t have a huge effect on stuff.

We see the same story with horizontal movement.

If you’re wondering why the postseason movement averages are so close to the major league averages listed below each table, that’s because of some of the decisions I had to make in classifications in order to compare these pitchers as a group. I lumped cutters together with sliders and splitters together with changeups, and two-seamers with sinkers, and knuckle curves with curves. It had to be done, and that obscures how generally awesome the stuff is with the short-rest pitchers.

There are a couple caveats to this. We don’t know what the impact of short rest is on command. And then there’s multiple short rest starts. Three times in the PITCHf/x era, a pitcher has gone on short rest twice in the same postseason, and the average velocity drop in the second short rest appearance was just short of a full tick on the gun. This is the first time, according to the play index on Baseball Reference, that we’ll have a pitcher go for a third short rest start in one postseason in the PITCHf/x ERA. Kluber will break new ground.

But at least it looks like, even on short rest, the postseason starter’s stuff is just as awesome as it was in the regular season. Given that we know there’s a postseason velocity bump, we can probably attribute this similarity in stuff to the same source: those butterflies pumping away in their stomachs as they take the mound. Adrenaline: it’s a heck of a drug.