First-Pitch Strikes, Plate Discipline and Players Due to Bounce (or Fall) Back: Part 1

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

Player	F-Strike%	ExF-Strike%	Difference
Albert Pujols	48.0%	55.4%	7.4%
Alex Rios	52.7%	57.0%	4.3%
Alfonso Soriano	55.8%	60.0%	4.2%
David Ortiz	49.5%	53.3%	3.8%
Evan Longoria	52.7%	56.5%	3.8%
Alberto Callaspo	52.9%	56.6%	3.7%
Billy Butler	52.2%	55.7%	3.5%
Adrian Beltre	57.3%	60.7%	3.4%
Victor Martinez	53.7%	56.4%	2.7%
Juan Pierre	55.6%	58.3%	2.7%
Angel Pagan	55.3%	57.7%	2.4%
Aubrey Huff	53.7%	56.0%	2.3%
Brian McCann	53.0%	55.1%	2.1%

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

Player	F-Strike%	ExF-Strike%	Difference
Colby Rasmus	58.4%	54.8%	-3.6%
Erick Aybar	63.2%	59.6%	-3.6%
Aramis Ramirez	62.7%	58.9%	-3.8%
Carlos Pena	58.4%	54.6%	-3.8%
Dexter Fowler	59.2%	55.3%	-3.9%
Cliff Pennington	60.4%	56.5%	-3.9%
Jason Bartlett	60.7%	56.6%	-4.1%
Hideki Matsui	58.1%	54.0%	-4.1%
Michael Bourn	59.0%	54.9%	-4.1%
Starlin Castro	62.9%	58.7%	-4.2%
Yunel Escobar	60.5%	55.6%	-4.9%
Hunter Pence	64.1%	58.8%	-5.3%
Drew Stubbs	62.1%	56.7%	-5.4%
B.J. Upton	63.8%	57.8%	-6.0%
Mark Reynolds	62.1%	56.0%	-6.1%
Yuniesky Betancourt	67.0%	59.9%	-7.1%

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.