Break versus Movement
As we all know by know the pitchf/x data is an incredible resource for baseball analysts. For each pitch thrown in a major league game we get scads of data, so much so that it is hard to even know where to begin. And once we have begun it is easy to just go with the flow of analyzing what others have analyzed. At the PITCHf/x summit Alan Nathan noted that one piece of information, the break of a pitch, is rarely looked at in pitchf/x studies.
In my posts when I have examined the movement of pitches I have used the word 'break', but done so incorrectly, using it to describe the movement of a pitch. So I thought it was important to make a post clearing up the difference between the two pitchf/x terms and make a preliminary examination of pitch break
MLB's GameDay calls movement: (images and descriptions from MLB Advanced Media here).
The Pitch-f/x or 'PFX' value is the distance between the location of the actual pitch, and the calculated location of a ball thrown by the pitcher in the same way but with no spin; this is the amount of 'movement' the pitcher applies to the pitch. A faster, straighter pitch like a fastball will have a higher Pitch-F/x value than a slower, breaking ball like a curveball.
As stated this leads to the counterintuitive result that fastballs 'move' more than curveballs. Here is a histogram of the movement of the four main pitch types.
Here his how GameDay defines the break of a pitch.
Break is the greatest distance between the trajectory of the pitch at any point between the release point and the front of home plate, and the straight line path from the release point and the front of home plate. Curve balls and sliders will have larger break value than fastballs. Pitch trajectories shown in blue indicate breaking pitches.
This leads to a more intuitive result that fastballs break the least and curves the most. Here is a histogram of the 'break' in inches of the four major pitch types.
In my posts where I have examined the results of a pitch by its movement I have exclusively used the PFX or movement value, which is often broken up into its vertical, pfx_z, and horizontal, pfx_x, correspondents. These are often used to produce the horizontal versus vertical movement graphs that are show the different pitch types of a given pitcher.
Since break is a more intuitive value I wanted to know if it did as well at predicting the results of a pitch as movement. Here I will just look at curveballs, which I assume is the pitch whose outcome is most impacted by its break.
Here is the run value (again negative is good for the pitcher) of a curveball based on its break, on the left, and movement, on the right. The gray indicates the error.
As you can see if you could choose just one piece of information, the break or the movement, of a curve in order to predict its success you would definitely choose movement. The error bars are smaller and non-overlapping. That is if you have a curve with 6 inches of movement it is quite likely to have a different run value than one with, say, 10 inches of movement. On the other hand if you have a pitch with 10 inches of break on average its run value is lower than one with a break of 14, but we are no where near as certain.
It is too bad, the intuitive value is not as good a predictor as the non-intuitive value. Still it is an interesting piece of information, which is currently not often reported or examined.