From: spira@panix.com (Greg "Sarcasm Is A Way Of Life" Spira)
Subject: Re: Statheads and park effects
Date: Sun, 20 Dec 1992 06:49:19 GMT
Organization: Boo!  

In <28591@optima.cs.arizona.edu> dkl@cs.arizona.edu (David K. Lowenthal) writes:


>I have a question for the stat people.  How can you justify this
>park effect thing?  In other words, for every park prediction made
>on the net, how many are correct?  Doesn't is seem like stretching
>it a little to say that a player with a different team will play at the
>same level with his new team in a new park?  Are players robots who you 
>can pick up and place in a new stadium and watch them do exactly the
>same things so that only the change in park matters?

Okay.  Very reasonable question.

First, the justification for evaluating a player's contribution to
his team with park effect adjustments is easy.  A run in the Metrodome
is just not worth as much as a run in the Oakland Coliseum because
runs are so much easier to come by in the Metrodome.  (This is fairly
intuitive, I think.  A single run in a game in which 15 runs are scored
is not worth as much as a single run in a game in which 5 runs are
scored.  Therefore, in a park are runs are less of a scarce resource,
each run created isn't worth as much).

Now this does not have all that much relation to how individual players
are affected by a park; this is about a player's value to his team.

Now it is perfectly possible that a hitter is not helped by a great
hitter's park.  Not likely, but certainly possible.  So evaluating the
effect of a park on a player is not quite so easy.  And when we
estimate how a player is going to adjust to his new surroundings,
we're making an educated guess, but we can't really say for certain.
And, of course, there are sometimes psychological changes when a
player like Gary Sheffield changes teams, and that has nothing to do
with the park.  And while I'm wary of most of the media's psycho-
gobblygook to explain changes in a player's performance that are easily
explained by more concrete factors or noise, it goes without saying
that some players will react a certain way to a new circumstance and
take that reaction on to the playing field with him.
 

>Before last season, several netters and I engaged in a "discussion" of
>how Greg Swindell would do with the Reds.  He came from a huge park,
>Cleveland, and went to a homer haven, Riverfront.  He posted an upper
>3's ERA with Cleveland the previous year.  I was scorned, especially
>by Valentine, when I suggested his stats might improve because he was
>playing for a better team, even though the park effect would suggest
>a downward trend.  Netters predicted a mid 4 ERA for him given the 
>park change and his tendency to give up homers.  He ended up with
>a mid to high 2's ERA.

And the best year of his career.  Predicting what pitchers will do is
always a very tricky business whether the pitcher changes parks or
not.  And it's not that unusual to see a pitcher in a hitters' park
which should be terrible for him end up with an ERA at home over 1 run
better than on the road over a year or two.

If Swindell had stayed in Riverfront for 3 or 4 years, I'm almost
certain his stats would have reflected thefact that Riverfront would 
raise his ERA and have more of an effect on him than it would a
pitcher who gives up more ground-ball outs.           

>Obviously this is only one example.  But all i am asking is can you throw
>around park effects like they are gospel?  What percent of your predictions
>are correct?  Players can adjust to new surroundings, and stat people
>don't consider that.  These kind of things are called "intangibles", 
>or *luck* by Ms. Nichols.  For example, can't a pitcher who just pipes
>the ball because he pitches in the Astrodome start nibbling the corners
>when he gets traded to Riverfront?  Can't a hitter who hits 20 homers
>in Oakland take one look at the short Yankee porch and hit fewer homers
>because he wants to pull everything (cf. Dave Revering)?

Can it happen?  Sure.  There are clearly hitters who learn to take
special advantage of their home parks.  But I think that their styles
have to already be oriented in that direction.  In other words, a left
handed pull hitter might adjust to get a little more out of Yankee
Stadium than his current style permits.  But most hitters aren't going
to be able to do that; they would have to change their hitting style
in such a way that it would probably mess their whole game up bad.
Wade Boggs, for example, is really unlikely to be able to do much with
the Yankee Stadium short porch.  I'd bet anything that his home/road
splits won't be anything like they were at Fenway over the next 3
years.  And I'd bet anything that if Joe Carter had gone to KC, 
there's just no way he would've turned into a line drive hitter
to adjust to the park.

I don't think this really has anything to do with the intangibles
debate, by the way.  Or luck.  This is very tangible stuff.  The
thing you have to realize when you look at the data is that there's
a lot of noise, especially for pitchers

Before I go, let's take a look at pitchers who have spent most
of the last 5 years in great hitters' parks.

        Home     Road
Clemens 2.77     2.48
Rijo    2.80     2.38
Maddux  3.11     2.92
Glavine 3.58     3.44
Browning4.23     3.36
Smoltz  3.36     3.64    

These are the only guys I could think of with that large a sample
size in a great hitters' park.  Now, remember, there is a home
field advantage, and the average pitcher posts an ERA of, oh,
about .15 lower at home.  Yet all these guys but Smoltz have posted better
ERAs on the road.  You will occassionally
find a pitcher doing better at home in a hitters' park over a long
period of time, but it won't happen all that frequently. 

The main question I think you're asking is if our predictions work
better with park effects than without.  And I can tell you that, yes,
the average projection/prediction is more accurate if you take park
effects into account.  That doesn't mean that the prediction will
always be more accurate, but it will much more often than not.

Greg 

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