Who gets the credit/blame for that home run?
February 6, 2008 4 Comments
Do hitters hit home runs, or do pitchers give them up? Of course, the answer to that question runs both ways, but who is more to blame/credit? Pitchers occasionally throw such beautifully tantalizing hanging curveballs that even Rafael Belliard hit the occasional home run and some hitters are so strong that they can punish the even the best-placed pitch. But it brings up an interesting question. Who is more in control of how far the batter hits the ball? After all, a home run is simply a fly ball that went a long way and crossed over a fence.
Here’s how I (sorta) answered the question: From 1993-1998, Retrosheet’s data files contain pretty good data on hit locations, primarily because those years were compiled by Project Scoresheet and licensed to Retrosheet. Recent Retrosheet files are much more scant in this data. The way that Project Scoresheet made notations on the data was through the use of a standardized rough map of zones on a ball diamond. It’s rather rough-grained, but it takes us from being able to say that Jones flew out to center field to saying that Jones flew to shallow (or deep) center. Once we know where a fly ball went (and I selected out all balls from 1993-1998 which Retrosheet said were either pop ups or fly balls), in terms of what zone, we can get a decent appoximation of how far away that is from home plate.
I assumed that all balls attributed to a zone were hit to the exact center of that zone. Of course, that’s not true, but it’s close enough for government work (some were hit a little beyond, some a little in front… it evens out). Since the Project Scoresheet grid is meant to scale to the outfield dimensions of a park, we need to know the outfield dimensions of the park in use. (The infield dimensions of all parks are set by the official rule book). If one knows a little bit about trigonometry, it’s easy enough to get a decent guess of where the was hit to, if it was on the field of play. For home runs, I gave the hitter 105% of the wall measurement over which it crossed. (So, a HR hit to a 360 foot power alley was estimated at 378 feet.) 105% was nothing more than my guess.
I totalled up the mean estimated distance for all fly balls and pop ups hit in a season by each batter, and then turned around and sorted it by pitcher. I selected out only those with 25 fly balls in the season in question that they either hit or had hit off of them. I subjected them to an AR(1) intra-class correlation to look at the year-to-year correlations over the six years in the data set to see if the mean distance was more consistent for pitchers or for hitters.
ICC for pitchers = .312
ICC for batters = .612
Batters are fairly consistent from year-to-year in how far their average fly ball travels. Pitchers are less so, but still have some level of consistency from year to year. It seems that both share some blame/credit for the distance on a flyball. This might explain why batters seasonal rates of HR/FB were more stable than pitcher rates. For those unfamiliar with this methodology, you can interpret those numbers in much the same way as a year-to-year correlation coefficients (although this method is better, as it allows for multiple data points.) There are some batters who are powerful (i.e., they hit the ball a long way) and some who are not, and that power level is pretty consistent from year to year. Pitchers who give up fly balls (and all of them, save Fausto Carmona, occasionally give up a fly ball) do have some (not a lot, but it’s there) repeatable skill in whether they tend to give up short fly balls or long fly balls. For those GMs nervous about signing that fly ball pitcher because he might give up a bunch of home runs, you can check his average fly ball distance (and perhaps his standard deviation), perhaps look at it by field, and plug in a few numbers to at least give you a little better projection for how many HR he might give up next year, although the error of prediction is still likely to be rather high.
Let’s play around with this a bit more from the batter’s perspective. I looked at the average distances for balls hit to the batter’s pull field, opposite field, and center field. I upped the inclusion criteria to 50 FB in the season in question. Again, I looked at ICC over the six seasons in the data set. (Anything in the grid with an “8″ in it was “center field”, so that includes the power alleys.)
ICC for pull field = .239
ICC for center field = .591
ICC for opposite field = .359
Batters are much more consistent in how far they hit the ball to center field (and the power alleys), and are actually more consistent in how they hit the ball to the opposite field than to their pull field. So if you want to get a good idea of how a player will hit for power, take a look at what he does gap to gap. That’s going to be the most consistent measure.