Location, Location, Location
The location of a pitch is one important factor in determining its fate. If a batter swings at a pitch thrown low in the strike zone, he has a good chance of hitting a ground ball, while if he swings at a higher pitch, there is a greater chance of him hitting the ball in the air. A difference in location of a couple of inches can be the difference between a home-run and a shattered bat. Pitchers need to be able to throw to precise locations and hitters need to be able to recognize if a ball is going to be hittable. As you can probably guess by now, this article is going to focus on the location of pitches, in and around the strike zone.
Before I continue writing though, I need to mention something. John Beamer wrote an really interesting article earlier this week about the accuracy of the Enhanced Gameday data. Based on his examination of Kevin Millwood, John found that the tracking systems were inconsistent across stadiums. However, the biggest problems that John found were regarding the release point and the ball as it left the pitcher's hand. The chart he showed of the strike zone showed no stadium-to-stadium bias, which bodes well for my current article. I think the differences with release points are caused by difficulties aligning the cameras the same at different stadiums without a consistent reference point, but home plate should serve as a good landmark in every stadium to align the cameras for the strike zone.
John looked at the spread of pitches and thought they were random enough not to worry too much about a stadium bias, but I can do a little checking too. Enhanced Gameday provides an x,y location, tracked by the camera system, of pitches as they cross the plate, as well as an x,y location entered by a human stringer. The stringer enters the location where he thinks the ball crossed the plate. Here's a plot of the X coordinate for the computer generated values vs. the human entered values.
As you can see, it's a pretty good match overall. I'm not looking for a 100% match, and I don't totally trust human entry on this either, as it's pretty tough to actually tell where the pitch was when it crossed the plate, so I'm comfortable using the camera-tracked values in this case.
Getting back to the article, lets look at where right handed pitchers throw to right handed hitters. Of the 11,109 pitches I have from these confrontations, here is where they all ended up. The strike zone is the red box in the middle and the graph is from the catcher's perspective. The numbers in each grid are simply the number of pitches thrown in that region. I didn't convert these into percents because the raw numbers give a sense of the number of pitches I have for each split. The chart is cropped on the sides and the bottom to focus on pitches that were near the strike zone.
It's nice to see that most of the pitches are located in the strike zone. This seems obvious, but it serves as another quick check on the accuracy of the data. I liked the simplicity of this layout and some basic trends pop out right away. Right handed pitchers work away from right handed hitters, and when they work outside the strike zone, it's typically low and away. They throw below the strike zone more than they throw above it.
Digging a little deeper, the three regions just off the plate on both sides (three inside and three outside) are interesting. At each height, there were more pitches outside than inside, but as the height increases the number of inside pitches remains relatively constant and the amount of outside pitches decreases. I have no idea if this is an artifact or an actual pattern, so here's the same graph, but for left handed hitters.
For left handed hitters, pitchers again threw more pitches outside, and were more inclinded to throw pitches below the strike zone than above it. As the height increases with a left hander at the plate however, there is more of a chance of an outside pitch. Do these trends exist when left handed pitchers are on the mound? Here are the two charts for left handed pitchers, but there doesn't appear to be much of a continuation of the trend. The other trends about working outside and below the strike zone also don't seem as clear, if they exist at all.
It's nice to know where pitchers threw the ball, but what actually happened to those pitches when they reached home? Focusing on right handed pitchers throwing to right handed hitters, here is a chart showing the percentages of pitches in each region that are swung at.
Right handed hitters swing at anything in the strike zone, except pitches down and away. Those pitches are strikes but hitters will swing at them only half the time, similar the frequently they chase pitches in regions abutting the strike zone. My guess is that right handed hitters as a group are unable to drive the low and away pitch, so they don't swing at it. They can afford to take the pitch if they don't have two strikes. However, right handed pitchers have figured out that right handed hitters don't frequently swing at that pitch and consequently throw to that region more than any other region. Hitters may not swing at pitches in that region because they feel they are balls, although of the 406 pitches not swung at in that region, 69% (282) were called strikes. When hitters put pitches from that region into play, they had a .298 batting average on balls in play, which surprisingly isn't the lowest BABIP for pitches in the strike zone. Perhaps low and away isn't a utopia for pitchers after all. If fewer than half of right handed hitters swing at a strike, the only hitters who do swing at that pitch must be confident they can get a hit out of it, resulting in the average BABIP.
One surprising item on this chart is that the BABIP for pitches right down the middle is not the highest. Three corners are all hot zones for right handed hitters as a group. One explanation for the lower than expected BABIP is if 70% of pitches down the middle are swung at, a lot of those swings will be taken by bad hitters, swinging because of the location, as opposed to the pitch low and away, where the only hitters who swing at it know they can hit it.
The swing percentage and BABIP charts for left handed hitters facing right handed pitching are below. When left handed hitters face right handed pitchers, they think they can hit the pitch that is low and away, but despite swinging at it 59% of the time their BABIP is only .238. The location must be especially tempting for left handed hitters to get those results and continue swinging at it. Not surprisingly, right handed pitchers threw the second most number of pitches to that region. Lefties also appear to be vulnerable up and in, but right handed pitchers haven't targeted that area yet. Another interesting detail on the swing percentage charts is that despite a difference in the distribution of swings, both left handed hitters and right handed hitters swung at 63% of pitches in the strike zone.
Before I wrap up the article, I should mention that I do have the left handed pitching versions of the Swing Percentage and BABIP charts, but I don't have enough pitches in each region to draw any real conclusions from them, so I didn't include them. Even with the graphs I did use, I would feel more comfortable making the statements I made with a full season of data to back me up.
I learned a couple of interesting things while writing this article though. I had no idea how frequently batters swing at pitches in different areas of the strike zone. I knew roughly how much batters swung, but to actually see where they swing at pitches is pretty cool. With enough data, I would like to expand those charts, and do them for individual players. I would love to see what Vladimir Guerrero doesn't swing at or where someone like Scott Hatteberg swings. Are some pitchers able to consistently get batters to swing at pitches that aren't in the strike zone? I also learned that left handed and right handed hitters as a group have different holes in their plate coverage. Right handed pitchers as a group were able to exploit the aggressiveness of left handed hitters and throw pitches to an area where the batters couldn't hurt them. The pitchers were also able to exploit the passiveness of right handed hitters and throw pitches in an area of the strike zone where there was a smaller probability of the batter swinging. Maybe pitchers aren't as dumb as people think.