Jake Peavy has been a fantastic success so far this season. Using a fastball that sits in the high 90's, a slider that breaks in on right-handed hitters and a changeup that breaks the opposite direction, Peavy has dominated the National League. A more accurate statement would be that he dominated the National League in May, allowing only three earned runs in 34.0 innings pitched, with opponents hitting just .164 against him. Even outside of May, Peavy has done very well this season, so what can the Pitch f/x system tell us about him and his pitches?
Here's a chart showing Peavy's start on May 27th vs. the Brewers. He threw all four of his pitches in this start and you can see the different breaks that they have. His fastball and slider both break toward a right-handed hitter, while his changeup moves away from righties. His curve is a standard curve from a right-handed pitcher and runs away from a right-handed hitter. There really isn't anything particularly special in this chart, and I put it in to get a feel for his pitches. In this article I'm going to examine when during a game Peavy throws his pitches, and specifically, does he pitch differently in high pressure situations or low pressure situations?
Before I could look at when Peavy throws his pitches I needed to classify them. As I was classifying the pitches it appeared that he had five pitches. However, when I looked at data from individual games, I could only find evidence for four pitches, the fastball, slider, changeup and curveball. I was pretty confident that he only threw those four pitches, but there was clearly another group in the season graph.
This wasn't a case of stadium variation, as all these games were in San Diego, and they were all prior to June 4th, which was when MLB.com began varying the "release point" distance. After another round of looking at the data from individual games, I found two problems. One was pitches that weren't classifiable. These pitches had similar movement to Peavy's fastball, but the velocity was much slower. I'm not sure what caused this, and I removed them from the data set, but it just serves as another reminder to be careful with these data. The second problem I ran into was that Peavy had some serious variation in how his pitches moved from start to start. This is pretty different from what I found in my last article, and I'm not sure what it means. There were some patterns where every pitch in certain starts varied the same amount, which would indicate a camera change, so the differences might just be another reminder to be careful. However, for the purposes of this article, variations between starts don't matter as long as each start is consistent with itself, which was the case for the starts I examined. I ended up using Peavy's starts from 4/30, 5/11, 5/16, 5/22, 5/27, 6/7 and 6/19. Here is a table showing the percentage of each pitch that Peavy throws overall.
Pitch Total Mix
Fastball 417 0.61
Slider 159 0.23
Changeup 98 0.14
Curveball 11 0.02
Total 685 1.00
The chart is very basic, but one thing that stuck out to me was that Peavy throws his fastball 61% of the time, which initially seemed like a lot of fastballs. However, after comparing him to other hard throwing right-handers, such as Josh Beckett (61% fastballs) and Justin Verlander (65% fastballs), 61% seems about right. How often does Peavy rely on his fastball when the pressure is on though?
Once I had all Peavy's pitches classified I matched them to the Leverage Index that they were thrown in. I assigned the Leverage Index (LI) at the beginning of a plate appearance to any pitch thrown during that plate appearance, with steals and other runner advancements during the play being accounted for. I split up Peavy's pitches into those that he threw when the LI was greater than one and when it was less than or equal to one. One is defined as average LI, so I'm splitting Peavy's pitches into above average (high) pressure situations and below average (low) pressure situations. Here are Peavy's LI splits according to his pitches.
High Pitches Mix | Low Pitches Mix
Fastball 133 0.56 | 284 0.64
Slider 76 0.32 | 83 0.19
Changeup 25 0.11 | 73 0.16
Curveball 4 0.02 | 7 0.02
Total 238 1.00 | 447 1.00
You can see from the table that when the pressure is mounting, Peavy relies less on his fastball and much more on his slider, throwing it 32% of the time in high pressure situations, compared with just 19% in low pressure situations. Nearly half of all sliders that Peavy threw in my sample have come in high pressure situations, while just one-third of all his fastballs came in high pressure situations. In every game that I examined, Peavy's ratio of fastballs to sliders was smaller in high pressure situations compared to low pressure situations, as he threw 3.4 fastballs for every slider in low pressure situations, but only 1.8 fastballs per slider in high pressure situations.
I was a little surprised that Peavy used his slider so much more in pressure situations. One reason for the difference could be that in low pressure situations, Peavy is more focused on getting quick outs and using more fastballs to do so. The fact that he used his slider more in pressure situations isn't surprising, but I was surprised by the magnitude of the shift. However, without someone similar to compare him to I wouldn't know if he really went to it more or if that was a pattern all pitchers shared. I used the other starting pitcher in the All-Star Game, Dan Haren, as my comparison. Haren relies on three pitches, a fastball, a slider and a split-fingered fastball, with a very occasional changeup and curveball mixed in. Here's a chart for Haren showing the same pressure situation splits.
High Pitches Mix | Low Pitches Mix
Fastball 128 0.44 | 280 0.57
Slider 76 0.26 | 100 0.21
Splitter 82 0.28 | 92 0.19
Changeup 4 0.01 | 13 0.03
Curveball 0 0.00 | 2 0.00
Total 290 1.00 | 487 1.00
Whatever Peavy is doing with his slider in pressure situations, Haren is doing something very similar with his slider and splitter. Haren threw 28% splitters and 26% sliders in high pressure situations, compared with 19% and 21%, respectively, in low pressure situations. The ratio of Fastballs/Sliders and Fastballs/Splitters shows the same inverse relationship with pressure for Haren that it did with Peavy. One thing that really jumps out from these splits is the "out" pitch for each pitcher, not necessarily their best pitch, but the one they rely on to get outs. Looking at the basic chart, Peavy threw 61% fastballs, which makes it seem like that was his out pitch. However, he went hog-wild with his slider in pressure situations because that is his true out pitch. Haren relied on both his slider and splitter in pressure situations and used both of them for outs.
Both Peavy and Haren have different patterns that they follow when pitching in high and low pressure situations. Both pitchers use their off-speed pitches more in high pressure situations than in low pressure situations. This seems like it would be the norm in the Major Leagues, as pitchers would rely more on fastballs in low pressure situations, possibly to avoid walking batters and turning low pressure situations into high pressure one, and possibly to avoid showing their out pitches to batters. However, I can't know for certain whether Peavy or Haren throw a relatively high percentage of fastballs in low pressure situations because I don't have the Major League average for fastballs thrown in low pressure situations. That would need to be calculated before this type of analysis goes much further. With the MLB averages for the types of pitches thrown at different levels of pressure, game theory could be applied to the analysis, and statements like "Jake Peavy throws too many (or too few) fastballs in high pressure situations" would have real meaning.