Command PostDecember 23, 2007
Winter Wonderland
By Joe P. Sheehan

John Walsh wrote a fantastic piece on Thursday about the differences between fastballs, sliders, changeups and curveballs, and what happens when those pitches are put in play. I've done some research into this area myself and wanted to graphically present some of my findings.

One point that John made was fastballs, especially non-sinking fastballs, are hit on the ground the least often of any pitch. You can take this a step further, and look at the impact the location of a pitch has on how it is hit. The graph below looks at the percentage of each pitch type that are hit on the ground at different heights.


The most obvious thing is the huge advantage a sinker has in generating grounders compared to any other pitch. (I found sinkers the same way John did, by using all pitches with a pfx_z value of less than 6 inches). This isn't surprising, but what was a little surprising to me is how the groundball percentage of every pitch decreases at almost the same rate with increasing height. I would have thought that certain pitch types, especially curveballs, would have been much better, relative to other pitch types, when they were thrown low in the zone vs. high in the zone. I thought a curve would have a higher ratio of gb% on low pitches to gb% on high pitches than other pitch types did. This wasn't the case, so maybe the idea of a high curveball being a terrible pitch isn't totally accurate.

To get a better idea of what happens to high curveballs (and all pitch types), I looked at the slugging percentage for balls in play (including homers) based on which region of the strike-zone the pitch was thrown to. The table below shows those slugging percentages for the three vertical sections of the strike-zone. (The averages at the bottom are only for the pitches in the strike-zone and are higher than the averages in Walsh's article.)

        FB     SL     CH     CB     Sinker | Avg.
Top     0.564  0.565  0.692  0.579  0.580  | 0.596
Middle  0.622  0.590  0.612  0.559  0.558  | 0.588
Bottom  0.554  0.496  0.498  0.458  0.481  | 0.497
Avg.    0.580  0.550  0.601  0.532  0.540  | 0.561

For pitches low in the strike-zone, batters have the lowest SLGBIP against curveballs, but if a curve is thrown at the top of the strike-zone, batters greatly increase their SLGBIP. Curveballs are hard pitches to hit, but the difference in SLGBIP between a low curve and a high curve is second only to the difference between a low changeup and a high changeup. Everything else being equal (speed, spin, movement, expectations of the batter, if the batter swings, etc.) a pitcher is increasing the batter's SLGBIP by roughly .100 points if he throws a curveball that isn't at the bottom of the strike-zone.

A changeup is potentially a great pitch, but changeups that aren't at the bottom of the strike-zone are hit much better than average. Low changeups are hit about as well as low sliders, but as the two pitches are elevated, the changeup gets hit much harder than the slider. A changeup above the knees is essentially a meat-ball and by throwing a changeup that isn't down in the strike-zone, the pitcher is increasing the batter's SLGBIP by at least .115 points.


Those slugging percentages seem quite high to me. What is the average SLG% on a BIP? The median team average SLG% is in the neighborhood of .419. Yet no slugging percentages in any part of the strike zone are that low? I'm probably not understanding something.

CJ: it makes sense. BIP factors HR's and K's out. Since there are many, many more strikeouts than HR's, all offensive numbers (BABIP and SLGBIP) are going to be vastly higher than overall numbers when only considering balls in play. Just like BABIP is way higher than BA, SLGBIP is way higher than SLG.

The SLG% on BIP are perfectly reasonable. It seems high, but it's not in actuality.

RS, the article says that the SLG% includes HRs. Since BABIP might average 30-40 points higher than Batting Average, my initial reaction was that the ratio of SLG-BIP to SLG was higher than BABIP to BA. But I read the linked Walsh article, and the BABIP average is what I would expect, while the SLG-BIP was similar to the table in the my initial reaction probably was wrong.

Also, if I understand this article correctly, the SLG average is only for balls in play in the strike zone. Presumably, balls in play outside the strike zone are much more likely to be outs. So that could explain it a bit more for me.

Major league SLG last year when not striking out was .523.

It's worth keeping in mind that the PITCHf/x sample is skewed heavily toward the last three months of the year. In addition, the data from the first three months of the year was mostly gathered from 8-9 stadiums, and other stadiums came online mostly throughout the month of July. So we certainly don't have a perfectly unbiased sample of data. I don't know if that would account for .038 of SLG, or whether Joe only used balls in play from pitches in the strike zone.

As Joe stated in the sentence directly above the table, "The averages at the bottom are only for the pitches in the strike-zone and are higher than the averages in Walsh's article."

Slugging averages on balls in play from outside the strike zone would certainly be lower than pitches in the strike zone.

The note you make about the expectation that curveballs up in the zone would seemingly result in more GBs is probably not true due to the nature of the pitch. Most pitches when they are "left up" are the result of the pitch not working. Thus, more likely for it to be hit in the air (and far).

Great work, Joe. The table is especially fascinating.

(And thanks for the kind words.)