Command Post September 07, 2007
That Sinking Feeling: Part Deux

Sinkers have been a popular topic for research with the PITCH f/x data so I'm going to that well once again and try to determine why sinkers are hit on the ground. One explanation given for why sinkers turn into ground balls is that sinkers are ordinary fastballs thrown low in the strike-zone, and pitches low in the strike-zone are more likely to be hit on the ground. This would mean that Derek Lowe's "sinker" is a similar pitch to Chris Young's fastball, but Lowe (and other pitchers with high ground ball percentages) frequently throw their fastballs low in the zone. Another possible explanation for the relationship between sinkers and ground balls is that there is something different about the flight of a sinker that causes a hitter to hit a ground ball when he puts it in play. This would mean that Lowe's sinker is actually a different pitch than a regular fastball, with hitters putting it in play on the ground, regardless of where it is thrown.

It is pretty easy to test whether there is something unique about the fastballs thrown by pitchers with low ground ball percentages (the amount of ground balls divided by all balls in play or GB%). I order to do so, I created three different groups of pitchers, based only on their GB% (the groups were pitchers with GB%>=.49 GB%<=.35, and all others) and looked for differences in their fastballs. After I had the pitchers grouped, I removed anyone I didn't have at least 450 total pitches worth of data. 450 pitches is a round, arbitrary number, but from eyeballing it, that was about the point where pitchers with only a couple of starts in Enhanced capable parks began to show up. The chart below shows a comparison between each group's average fastball.

Pitcher       MPH    Pfx_x   Pfx_z    Pitches   Group Size
Ground ball   91     -5.97   5.66     7385      16
Neutral       90     -2.95   9.14     29729     73
Fly ball      90     -0.80   10.71    4686      13

As a reminder, the pfx_x/z values are the horizontal and vertical differences between the actual pitch and a hypothetical pitch without spin. For ground ball pitchers, their fastballs end more than 5 inches higher than a spin-less fastball would, which might seem counter intuitive, except that every fastball ends up higher than a non-spinning pitch would, due to the backspin on a fastball. Fastballs thrown by neutral pitchers end 9 inches higher than a hypothetical pitch, so hitters are conditioned to seeing a pitch drop a certain amount between the mound to home, a distance that corresponds to ending 9 inches above a spin-less pitch. When a sinker is thrown, it drops 4 inches more than a "normal" fastball, so there is definitly something unique about sinkers and it makes sense that hitters would hit the top half of the ball and pound it into the ground.

If you followed that explanation, check out the chart again. If ground balls result from hitters expecting a pitch to be higher than it is, and hitting the top of the ball, fly balls seem to come from the opposite case. Rising fastballs, which are the opposite of sinkers, are fastballs that don't drop as much as "normal", due to higher amounts of backspin. A hitter will have an opposite reaction to a rising fastball compared with a sinker, as it will drop an inch less than a normal fastball does. The batter will usually hit the bottom of the ball, resulting in either a line drive or fly ball, but not a grounder. The actual values in the chart need to be taken with a grain of salt, due to tracking differences at different stadiums, but the overall pattern is there.

Now that we know sinkers are a unique pitch, it's time to test some of the other ideas from the first paragraph. Even though it is a unique pitch, the sinker could be thrown low in the strike zone, causing the ground balls. Below on the left is a chart showing what percentage of the 7385 sinkers in my sample were thrown to specific areas. There seems to be a slightly higher percentage of sinkers that end up low in the strike zone, compared both to all other sinkers and 'normal' fastballs (from the neutral group), but the differences don't seem to be anything too big, and pitchers with high GB% don't appear to throw their fastballs low in the zone any more than other pitchers.

A quick note about the charts, in the past when I have used graphs like this to show the location of pitches, I've always done so from the catcher's perspective. I've gotten several requests to show those graphs from the pitcher's perspective, which is how these are. Anyway, the chart shows where sinkers are thrown to, but is the location why the sinkers are turned into ground balls? Chris Constancio has already looked at this topic and while I only considered balls-in-play and used a different set of pitchers than Constancio, (and still have a relatively small sample) my conclusion is only slightly different.

Above is a chart showing ground balls as a percent of all balls put in play for each area. What you see is a wide range of outcomes, based on location, indicating that location does play a role in determining the outcome of a sinker. Sinkers thrown to the bottom of the strike zone are hit on the ground 60% of the time, which is comparable to Derek Lowe's GB%, while sinkers that are thrown at the top of the strike zone are hit on the ground 40% of the time, which is below league average.

However, in order to say that a sinker at the top of the strike zone results in less than an average amount of ground balls, you need to know what the average GB% is for each area. The chart below on the left shows the GB% of normal fastballs, which can serve as an average. This chart follows the same pattern as the sinker chart, where the height of a pitch influences the result and you can see that in every region, sinkers have a higher GB%. Even though the GB% for a sinker varies depending on its location, (and the percents are influenced by the small amount of balls in play), in every region sinkers are 20-30% better at getting ground balls than normal fastballs, as illustrated by the chart on the right. In fact, it looks like if you shifted the sinker chart down one set of boxes, it would line up pretty well with the normal chart. A sinker that ends belt high gets the same GB% as a regular fastball does when it ends at the knees.

So far we've looked at the PITCH f/x values of a sinker and what happens to it when it is thrown to certain areas. A sinker is a pitch with unique flight characteristics and is frequently thrown low in the strike zone, both of which contribute to very high ground ball percentages for sinkers. However, ignoring location for a second, the optical illusion that fools a batter into hitting the top of a sinker is only effective if it doesn't become the norm...so how does Derek Lowe keep getting ground balls?

Lowe only throws three pitches, a sinker, change-up and curve, and looking at the GB% for each pitch in the chart below, it appears that he has the highest GB% with his change-up. He gets more total grounders from his sinker, but on a percentage basis, his change-up is better at getting grounders. This is based on a sample of just 33 change-ups in play, so the numbers could be totally wrong, but if this phenomenon is real, it means that Lowe's change-up is really his ground ball pitch.

Pitch    GB%      # in play
FB       62%      122
CH       85%       33
CB       50%       32

Assuming for a second that Lowe's change-up is really his ground ball pitch, it might partially explain why hitters are unable to adjust to the sinker and keep pounding that pitch into the ground. Lowe's change-up has a vertical drop of 4.23 feet from release point to home, compared to a drop of 3.71 feet for his fastball. Does this 6-inch change result in hitters again being tricked into thinking a pitch was going to break less than it actually did and hitting the top of the ball? I don't know, and while most pitcher's change-ups have a greater vertical drop than their fastballs, not all pitchers get a higher GB% from their change-up than the fastball from that same pitcher.

Unfortunately the sample sizes in all these cases are very small, so the jury is still out. I am still curious though about how the Lowes of the world continue to get such a high percent of ground balls from their sinker. Wouldn't hitters eventually realize what's happening with the movement of a sinker and adjust their swings? MLB hitters are good as a group, so there has to be some reason for them to continue hitting sinkers into the ground.

The location of any pitch when it crosses the plate is related to what happens when it is put in play, and sinkers are no exception. Low sinkers are hit on the ground more frequently than high sinkers. However, regardless of where they are thrown, sinkers are hit on the ground more frequently than an average pitch in that same location. If I were to speculate, I'd say that the movement of a sinker is more important than the location because wherever a sinker is thrown, its gets more grounders than a normal fastball. I think batters have a tough time adjusting to the break of a sinker, and if the pitch is thrown low, it just increases the chances of a ground ball.

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That's pretty much the end of the article, but after looking at sinking fastballs and rising fastballs for several days, I got curious and wanted to see who had the highest and lowest GB% when they threw a fastball. The chart below just looks at fastballs that were put in play (min. 50 fastballs) and has some cool results.

Name             GB     BIP     GB%
Zach Miner       38     57      0.67
Sergio Mitre     48     73      0.66
Felix Hernandez  83     128     0.65
Kameron Loe      47     73      0.64
Tim Hudson       74     118     0.63
====================================
Rich Hill        24     98      0.24
Ted Lilly        19     95      0.20
Chris Young      15     70      0.21
Barry Zito       12     62      0.19
Chuck James       9     61      0.15

While most pitchers have a similar overall GB% and fastball GB%, Kameron Loe has an overall GB% of 53%, but with his fastball, he gets ground balls 64% of the time. On the other side of the spectrum, Chuck James has an overal GB% of 29%, which drops to 15% on fastballs. Looking at the full list, you can get a better sense of how some pitcher's achieve their results.

I created another table along with the ground ball table that shows the percentage of fastballs that were swung at and not put in play (the batter either missed the pitch or fouled it off).

Name             SW    Foul    BIP    Not in play%
Takashi Saito    33     31     16     0.80
Jose Valverde    26     42     21     0.76
Johan Santana    26     71     30     0.76
Tony Armas        8     52     19     0.76
Jake Peavy       43    156     71     0.74
Huston Street    11     37     19     0.72
Scott Kazmir     29     39     27     0.72
Frank Francisco  23     47     28     0.71
Brandon Morrow   34     55     36     0.71
C.J. Wilson      30     36     28     0.70
==========================================
Dustin Moseley    8     50     79     0.42
Tom Glavine       4     37     56     0.42
J.D. Durbin       3     31     48     0.41
Lance Cormier     5     18     33     0.41
John Lannan       3     21     35     0.41
Kason Gabbard    17     26     66     0.39
Oscar Villarreal  2     26     44     0.39
Sergio Mitre      9     36     73     0.38
Livan Hernandez   6     46     87     0.37
Matt Morris       9     31     76     0.34

I made this chart just for fun, but eventually I want to be able to look through all pitch types and find who has the most unhittable (or ground ball inducing) pitch, rather than just fastballs. With that list, you can get more nuanced results and really compare things like whether Saito's fastball or Santana's change-up gets more swings-and-misses.