Back in September, Bill Petti at Beyond the Boxscore took a look at the year-to-year correlations of a set of hitting metrics. Some of the stats you’d expect had no year-to-year staying power (AVG, BABIP); some you would think are skill based turned out to vary greatly (Line Drive Rate); while some metrics proved to be remarkably consistent (Contact Rate, Swinging Strike Rate).
What jumped out to me was that First-Strike Rate had only a .56 year-to-year correlation for batters, while all of the stats I’d expect to directly impact First-Strike Rate (Swing Rate, Contact Rate, etc.) were quite consistent. First-pitch strikes make a huge difference in any at-bat, and the high year-to-year variation in this stat suggests that, over the course of a season, some hitters may have very good or very bad luck in this area. After looking at Petti’s analysis, I looked deeper into the phenomenon of F-Strike% and have three posts coming – starting with this one looking at my methodology and the basic information I found.
We hear announcers talk all the time about the ability of a pitcher to throw first strikes, and with good reason. In 2004, Craig Burley did a study on how hitters fare in each count and found that batters who face a first pitch ball hit .280/.385/.459 while those facing first pitch strikes hit just .261/.296/.411. In other words, a first pitch strike is pretty devastating to a hitter.
Combining Petti’s data with Burley’s study, it seems that hitters facing a high first-strike rate in a given year –- or at least higher than expected based on their underlying skills –- had some bad luck and probably performed worse than he could have.
To figure out if a guy faced too many or too few first pitch strikes, I had to start by figuring out how many they were expected to see. Taking a league average won’t suffice, as there are too many characteristics of individual hitters that impact first pitch strike rate. For example, a free-swinger is far more likely to hack and miss on any pitch (first or otherwise), and therefore should face more first-pitch strikes than a patient hitter. Sure enough, Nick Swisher faced around 54% first-pitch strikes the past three years; Vladimir Guerrero was over 60%.
To account for this, I used regression analysis to find a rough equation for what I called Expected First Strike Percentage or ExF-Strike%. I used five years of plate discipline stats for all players who qualified for the batting title. This gave me a total of 771 individual player seasons, with Swing%, O-Swing%, Z-Swing%, Contact%, O-Contact%, Z-Contact%, Zone%, SwStr%, and -– of course -– F-Strike%.
I ran a series of regressions with F-Strike% as the dependent variable and a variety of combinations of the other stats at independent variables. Based on these, I created five equations for ExF-Strike%, and tested each of these against 2010 plate discipline stats to see which equation was most accurate (if anyone cares, I used the sum of squared residuals to figure out which equation was most accurate). In the end, I stuck with an equation using all the plate discipline stats, as this was both the most accurate and explained the largest amount of variation in F-Strike%.
My next step was to compare F-Strike% to ExF-Strike% and find the outliers – guys who saw far more or far fewer first pitch strikes than expected. My assumption would be that the outliers in 2010 would see regression in their F-Strike% in 2011, leading to changes in performance. For the purposes of measuring offensive performance, I decided to use wRC+.
Guys Who Saw Too Few First Pitch Strikes
These were the 13 players (among those who qualified for the 2010 and 2011 batting title) who saw more than 2% fewer first-pitch strikes than expected. Of these 13, nine saw fewer first pitch strikes in 2011, as we’d expect. Ten of the 13 had a lower wRC+ in 2011. On average, they went from a wRC+ of 123.4 to 112.8 – a pretty significant drop.
Guys Who Saw Too Many First Pitch Strikes
These were the 16 players (among those who qualified for the 2010 and 2011 batting title) who saw more than 3.5% more first-pitch strikes than expected. Exactly the opposite of the list above, 12 of the 16 saw more first pitch strikes in 2011 and 10 saw their wRC+ go up. As a group, they went from 99.5 to 106.1 – not quite as big an increase as the decrease above, but still a significant change.
This, of course, is hardly a comprehensive study. However, there are very clear indications that for players with the largest gap between how many first-pitch strikes they should expect to see and how many they actually see, there is some ability to predict a regression in F-Strike% the next year and a related regression in overall offensive performance.
Next week, I am going to apply my ExF-Strike% formula to 2011 players and offer up some thoughts on guys who could rise or fall in 2012.
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