[情報] Is Jorge Posada a Bad Game Caller?
http://tinyurl.com/nqdl2t
One of the topics that has been coming up this season is Jorge Posada's
pitch-calling and how it is a problem. Most of the analysis on this is based
on comparing the Yankees' ERA with Posada behind the plate versus his backups.
Any analysis based on that premise is deeply flawed, because it assumes that
the distribution of innings between Posada and his backups include the same
pitchers in the same percentages, which is obviously not realistic or true.
Also, ERA can be impacted by things that are not directly in control of the
batter or pitcher.
That doesn't mean we can't look at the question, it just means that to do it
right a little more rigorous work needs to be done.
In the 2008 Hardball Times Annual, Tango Tiger wrote an article titled With
or Without You. The article was focused on Derek Jeter and basically looks at
how the team did with or without Jeter for the period in question. Without
getting into the Jeter/defense thing again, the methodology that Tango used
is ingenious and can be applied in a lot of different ways, even if we must
acknowledge it is slightly limited due to sample size issues and random
noise. Retrosheet's play by play files allow us to do the WOWY studies for a
lot of different criteria.
So let's take a look at Posada versus his backups using the WOWY methodolgy.
Here are the steps that I followed to do this.
1) Pull in all Yankee Retrosheet play by play data from 2000-2008. Although I
have the data to go back past that, I think nine years is enough data,
especially if we are trying to ascertain that there is a skill component
here. It's probably folly to assume that a player's skill remains static in
any area over nine seasons, much less more than that. Since 2009 play by play
data is not availabe in an easily parseable format right now, I can't look at
that.
2) Separate the data into batters faced with Posada catching versus everyone
else.
3) MATCHING INNINGS. This is the key part of this analysis. If you don't
ensure that you are weighing the contributions of each pitcher similarly, you
are not controlling for possible selective bias, like a good pitcher having a
personal catcher. To match innings, I simply pro-rated the larger sample to
the smaller sample. For example, Mike Mussina faced 998 batters without
Posada catching and 2183 with him, so Mussina's stats for both splits get
pro-rated to 998 batters.
4) Add it all up and see what comes out.
First, here are the straight totals before matching innings. I am looking at
the data in terms of how opposing hitters have done versus the Yankee
pitchers, so the numbers you see are the numbers they allowed to hitters.
Here are the splits with Posada and others for every pitcher who has pitched
for the Yankees from 2000-2008.
Matching those innings up, we get the following totals.
There's a difference there. The next question we have to ask is if the
difference is statistically significant. I'm just going to look at wOBA.
Posada's actual performance is a little worse than one standard deviation
from his backups. The difference in runs given a wOBA of .332 vs. .324 over a
full team season (4100 PA outs) is in the area of 30 runs. That's pretty
significant. I'm not sure I trust these numbers based on Keith Woolner's far
more exhaustive study that showed game-calling was NOT a statistically
significant skill. But that's what these numbers say.
I wouldn't call this proof that Posada is a bad game-caller, but it is
possible evidence that he may be worse than average in that regard.
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