March 7, 2017
Is Defense Slump-Proof?
Some days, we all wake up on the wrong side the bed. It starts to be a problem when your bed is against the wall. Slumps are a part of baseball (and life), because humans are creatures of cycles. Sometimes you’re caught in a bad one.
Slumping is the flip side of the “hot hand” coin, and so it’s going to get second looks and long stares around these parts. We know that there are situations in which a hitter goes 0-for-12 over the course of a few days, but is that “slump” a reflection of him having a few days in which he's actually a worse hitter than he normally is or is it simply a case that sometimes you get a few tails in a row even on a 50/50 coin? Could it be that sometimes it’s a little from Column A and others it’s a little from Column B?
Here’s the problem mathematically: Let’s assume for a moment that there really are days-long periods when a player just doesn’t have it. If we were to somehow do a blood test for hitting ability on those days, we’d find that he’s a .167 hitter that day even if he’s a .300 hitter overall. The next day, he’s still reading as a .167 hitter on the blood test and he performs that way.
Well, there are going to be other days-long periods when there’s nothing wrong with him and that blood test would say “.300 hitter” but he just happens to go 2-for-12. The next day, because nothing’s wrong, we continue to expect him to be a .300 hitter. There are going to be enough of each that we aren’t going to be able to sniff out which of those days-long periods are “slumps” and which are random noise.
If a slump were to go on for two weeks, we could start saying—mathematically—that it’s unlikely someone who was a true-talent .300 hitter could hit that poorly by chance for two weeks. But how many cold streaks actually last that long and where a hitter goes that cold? So, perhaps the problem with streakiness is not that it doesn’t exist but that it’s uniquely designed to avoid detection. We do have some evidence that these local variations can have some meaning and that it can actually tell us something about what to expect from a player going forward, but slumping is a tough one to pin down.
So, that brings us to fielding. Is defense slump-proof? There’s a general belief that while players might have weeks in which they are cold as liquid hydrogen at the plate, their defensive prowess is going to remain fairly steady over time. (For instance, this was what Cubs fans told themselves all last year about Jason Heyward.) A Gold Glover is always going to have a gold glove on his hand, right? And so, for players who are seen as streaky or volatile (and therefore, kind of a high-variance bet), the comfort is that even in those two-week stretches when they can’t hit anything it’s not affecting their defense.