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In Search of the Sinker

Fastball, curve, change-up. That's easy — oops, forgot one: slider. Oh, then there's the knuckleball, too. And the fastball isn't really just one pitch, is it? Splitter, cutter, two-seamer, four-seamer, sinker. Oy. There's the 12-6 curve, the backdoor slider, the frisbee slider. The circle change, forkball and the palmball, the screwball. What exactly is a knuckle-curve, anyway?

Lord knows there are many ways to throw a baseball and it's hard for the average fan to keep this catalog of pitch types straight. There's so much to know — 1) how does one throw these different pitches, 2) who throws what, 3) how do these pitches look to the batter, and so on. For those of a historical bent, like myself, you might wonder who threw what first. You know, somebody ought to write a book on this subject, just write down everything we know about pitches and pitchers.

Of course, somebody has written that book, two guys named Bill James and Rob Neyer, authors of The Neyer/James Guide to Pitchers. I highly recommend it to anybody who is interested in pitching, which is everybody, right? Actually, one thing that Neyer and James didn't investigate is how the different types of pitches look to the batter, and that's what I'd like to tackle here. I want to look at how these different pitches behave. What kind of movement do they have and how fast are they typically thrown. Once I've gotten a feel for the data, I'm going to dig a little deeper on the the sinker, a pitch that I have never understood very well.

I'm able to look at these things thanks to the pitch data that MLB collects for its Enhanced Gameday application. Several writers on the Internet have already started to delve into the wealth of information available: Joe P. Sheehan at Baseball Analysts was the first (to my knowledge) and Dan Fox (subscription required) (Baseball Prospectus) and our own John Beamer have also worked with the data. But, there is enough information available to keep at least a dozen analysts happy and I figure the more people looking at it, the better.

Investigation of pitch types — does a slider really slide?

I'm going to focus on pitch speed and pitch movement, because different types of pitches will generally have different speeds or movements or both. Pitchers also tend to be quite consistent in pitch speed and rotation, which gives rise to movement, from pitch to pitch (for a given pitch type, of course). This is not true with pitch location, which pitchers have less control over. Before we get into the nitty gritty, I need to define some terms that describe the movement of a pitched ball.

I will refer to two different quantities that measure how much a ball curves. The break of a pitch is the maximum distance between the trajectory of a pitch and a straight line that connects the starting and ending points of the pitch. In the graphic on the right, the break is the length of the red line segment.

Movement, on the other hand, is the term I use to describe how far a pitch moves compared to a hypothetical pitch thrown without spin. Look at the graphic and imagine that you are seeing an aerial view of a curveball. Had the pitch been thrown without spin it would not have curved, but rather it would have traveled along the blue dotted line. The length of the solid blue line segment is the movement on the pitch. Each pitch has a horizontal and vertical movement, which can be either positive or negative, depending on which way the ball moves. There is only one break, though, and being an absolute distance, is always positive.

Ok, let's look at some pitches.

Let's talk pitch type

Now we can start to examine this plot and and attempt to classify the different pitch types. Let's start with the green points: they are thrown above 85 mph and in fact, these are fastballs. They typically have a vertical movement of 10-15 inches and horizontal movement of 5-10 inches. Remember, these movements are as viewed by the catcher. Do these numbers make sense? Hmm, vertical movement on the fastball sounds right. But, since it's positive, does that mean Wolf's fastball is actually rising, against the claims of physicists across the land? No, because movement is measured relative to the same pitch thrown without spin. Such a pitch will drop on its way to the plate. Wolf's fastball will drop about 10 inches less than the hypothetical spinless pitch.

Does a fastball move horizontally, though? I have always thought that a fastball is thrown with backspin, in which case there should be no lateral movement. But this is only true for a strictly overhand fastball, while almost every fastball is thrown with an arm angle that is below straight-over-the-top. This imparts a sideways component to the spin, which causes the ball to tail in to the batter (for a right-handed pitcher and batter), i.e. it would have a negative horizontal movement. For a lefty like Wolf, the horizontal movement is positive.

Now, focus on the black points: these are thrown at less than 73 mph and break down and to the left (from the catcher's view): curve balls, obviously. Aside from some trick pitches (knuckleball, underhand pitches), anything thrown less then 75 mph is bound to be a curveball. Now, the red points: you can see that Wolf throws two different pitches in the high-70s, low-80s. The clump in the middle of the plot are sliders: relative to the fastball, they break down and to the left, just like the curves, but not as much. The red points in the upper right of the plot are change-ups: similar movement to the fastball, but thrown about 10 mph slower.

This business of identifying pitches strictly from the data is very exciting to an analyst, because it opens a multitude of possible things to study: how a pitcher (or batter) fares on any given pitch type; how pitchers choose what pitch to throw, given the batter, count and game situation, and so on.

The Mysterious Sinker

One pitch that has always fascinated me is the sinker. I can remember thinking as a kid: backspin gives the fastball that rise, side spin makes the curve ball break sideways, so a sinker must be thrown with overspin. That didn't seem right, though, because 1) the "overspin" ball is just an overhand curve and 2) seems like it would be difficult to throw a ball hard &mdash and sinkers are thrown pretty hard — trying to throw it with overspin.

It wasn't until years later that I understood what a sinker really is: it's a fastball that has less vertical movement than a typical fastball. Look, all pitches sink, in some sense. Every pitch ever thrown has dropped due to the force of gravity. The lift caused by the backspin on a fastball cannot overcome the force of gravity. We saw above that Wolf's fastball has a vertical movement of 10—15 inches. In other words, it drops 10—15 inches less than an otherwise similar pitch without spin. A sinker, as we'll see in a minute, is a fastball that drops about 5—10 inches more than a typical fastball.

The vertical movement for all fastballs (speed > 88 mph) in my pitch database are shown in the graphic on the right (black points). The green line shows the average relationship between pitch speed and vertical movement. Fastballs that are well below the line are "sinkers". Those light blue points are the fastballs from a single pitcher, can you guess who it is? Actually, it could be any number of pitchers, but it happens to be Roy Halladay, who has a world-famous sinking fastball and a nifty 55% ground ball percentage to go with it.

So, which MLB pitchers have the greatest "sink" on their fastball? To answer that question, I calculated the average vertical movement of each pitcher's fastball, which I defined as any pitch over 88 mph. The following table shows the top 15 pitchers ranked according to vertical movement.

Name                      Movement (in)
Meredith, Cla             -3.9
Moylan, Peter             -3.4
Feldman, Scott            -0.3
Halladay, Roy              2.9
Tavarez, Julian            3.0
Lowe, Derek                3.9
Loe, Kameron               4.1
Duckworth, Brandon         4.3
Wagner, Ryan               4.5
Cook, Aaron                4.6
Hernandez, Felix           4.7
Hudson, Tim                4.8
Webb, Brandon              5.1
Downs, Scott               5.3
Ortiz, Ramon               5.4

Just about every other guy on this list is known as a sinkerball pitcher, and most of them have high groundball percentages. Note that this is only a partial list, because not all ballparks have the equipment necessary to produce the Enhanced Gameday data. There are a lot of pitchers for whom little or no data is available. Note that these pitches are sinking between 5 and 10 inches compared to an average fastball. That's a lot, when you consider that a batter will swing through a pitch if the center of the bat misses the center of the ball by three inches.

I'm going to show you one last plot that demonstrates the connection between pitch vertical movement and ground ball percentage. To make the plot on the right, I took all fastballs that were put into play by the batter. I divided this data set up into four subsets, depending on the vertical movement of the pitch. The vertical movement of each subset is color-coded, from dark blue for the "sinkiest" pitches, to yellow for the "rising" fastballs. Each bar in the graph shows the percentage of a particular batted ball type (F, G, L and P mean fly ball, ground ball, line drive and pop up) yielded in that subset of the data.

You can see clearly that the groundball percentage varies strongly with the vertical movement on the pitch. Obviously, the F and P categories move in the opposite direction. Curiously, the line drive rate is about the same for all vertical movements.

But how do you throw the damn thing?

This is all very nice, but I must admit, it doesn't really help me understand how a sinker is thrown. Now, I realize that a two-seam fastball will have less "rise" on it than a four-seamer will, so maybe a sinker is just a two-seam fastball? It seems too easy, doesn't it? I mean, if it were just a case of holding the ball in two-seam mode, anybody could throw a good sinker, right?

To get some insight on that, I turned to the incomparable: Neyer/James Guide to Pitchers. In his article "The Mighty Fastball", Bill James writes

However, while some pitchers could make a ball hop and some people could make a ball "sink," there is no evidence of any major-league pitcher, before 1950, doing both, or switching between one and the other. ... Pitchers universally seemed to regard the movement of their fastball as a gift from the heavens.

Then, in the chapter "All the Pitches We Could Find," Neyer and/or James give two possible descriptions of how to throw a sinker. The first is just a two-seam fasty:

"Sinking fastball" is, today, synonomous with "two-seam fastball". Basically, grip the ball along — as opposed to across — the two seams, and throw like hell.

Hmm, maybe Alston's description is correct, but I imagine that this is a very subtle motion, especially when you consider that until 1950 or so, sinker ball pitchers were not even aware they were doing it.

John Walsh dabbles in baseball analysis in his spare time. He welcomes questions and comments via e-mail.




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