# The influence of batters’ expectations on pitch perception

Hi everyone. This is my first post on The Hardball Times Live and I’m really excited to have to opportunity to post here. I hope you enjoy my work. You can find more of my original research at my personal site.

What we’re going to look at today is the relationship between percentage of pitches on a certain count and batting eye by pitch type. You can read more about batting eye at my site but to summarize – it is a measure of how good the batter is at judging whether a pitch is in the strike zone.

Batters are obviously much less concerned with taking a strike when they have less than two strikes on them – and may choose not to swing at pitches which they know are strikes in these counts. Therefore looking at batting eye on most counts is an imperfect measure. For this reason we are going to look only at two strike counts for this analysis.

Unfortunately this gives us a mere four data points per pitch type, which means that the correlations I’m going to show you are based on a very limited number of points. On the plus side each point represents a few thousand pitches. Additionally, while this data is for the 2008 season, the numbers look very similar for 2009. I have also done a bit of follow-up analysis which will allow me to look at more of the points at the same time.

Let’s take a moment and think about what we might see in this analysis. I came up with a couple of different theories.

-You might suspect these measures are completely unrelated. After all a curveball is a curveball regardless of count and the batter should be consistent in their ability to tell if it’s going to be a ball or a strike.

-Perhaps pitchers can outsmart batters and throw pitches which the batters are not expecting.

Since I’m writing the article you can pretty much rule out the first theory and while some pitchers might be able keep batters off balance it doesn’t seem to be the case when we average over the league.

You might now conclude that the two measures are directly related – that the more frequently a type of pitch is thrown on a specific count the more a batter will be expecting that pitch type and the better they will read it. You’d be right – with one exception. Check it out.

We see that this strong positive correlation between percentage of pitches and batting eye exists for three of the four main pitch types. Batters seem to be better at reading fastballs, curveballs and sliders on counts where those pitches are more likely to be thrown. But what’s up with the change-up?

The change-up is generally thrown as a complement to a fastball. After seeing this data I thought that correlating batting eye on change-ups with percentage of fastballs thrown might be interesting. Here we see a pretty strong negative correlation.

I want to include one caveat here. Batting eye on change-ups also correlates strongly with percentage of sliders and curveballs thrown. In fact these correlations are a bit stronger. Comparing change-ups to fastballs makes the most sense to me intuitively, but the batter could just be looking for more off-speed pitches which might help them pick up change-ups.

Overall I think that there is ample evidence to support the following conclusions:

-Batters are better at judging whether a pitch will be a ball or strike on counts where they expect that type of pitch to be thrown.

-Batters do a good job of anticipating what percentage of each pitch type will be thrown on a specific count.

The one exception to these rules is the change-up, which batters seem to be better at picking up when they expect less fastballs (and more off-speed pitches.)

I’m really looking forward to delving deeper into baseball and the tendencies and strategies behind it. I hope you’ll enjoy reading my posts as much as I’ll enjoy writing them.

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Excellent work, Craig! Welcome to THT.

Wow, that is very cool, Craig. Thanks for the post.

This is over my head Craig. I’ll read this more in detail later tonight, so I can hopefully be on the same page as you!

It’s kind of technical and I’ve done a writeup at my site which I link to in the article which should help a lot.

If anyone has any questions please feel free to email me. I’m going to try to write up a little ‘101’ series as I get the time and post it on my site because it seems like a lot of people want to understand at a deeper level.

Craig, next stop: batting eye on sequence of pitches? For example, batting eye on CU that follow FB?

I definitely have sequence of pitches on my radar. I think my next article will be about selectivity (hopefully next week) but I’m definitely planning to look at sequence

Hey Craig: Thanks for reply. Can you post an explanation (or link) to your definition of batting eye? And an explanation of why it couldn’t be calculated for strikes alone (if that isn’t obvious from the definition)? I’ve spent a bit of time at your site, but couldn’t find a definition. Thanks.

This is probably the best explanation I’ve put up so far: http://sabometrics.com/?p=242 but you probably saw that.

Basically what batting eye is is the difference between your perception of strikes and balls. That’s why it can’t be calculated for just one or the other.

I think the fact that there is such a heavy correlation between %age thrown and batting eye is pretty strong evidence for my argument. Especially when you look at the z-scores and combine all the points.

I am planning to write up more of a 101 version of the theory as it applies to baseball. Hopefully that’ll help.

One additional point is that you are not penalized for swinging more. In fact swinging more at strikes actually improves your batting eye rating. It is the difference between % swinging at strikes and % swinging at balls which determines the rating. Not sure if that was clear or not.

A fixture at Chicago Bulls games for Michael Jordan’s career in the Windy City, Schmidt acquired many rare pieces of memorabilia from his career, including these game-worn “Cardinal” Air Jordan 7s from early in the 1992-93 season