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The
Mile High Effect & The Humidor Ball
(Aug-26-2007)
When I mentioned the players got it wrong in a recent poll about the
best hitting park, that it was still Coors Field and not the players’ choice
of Citizens Bank Park
in Philadelphia,
I got a thoughtful email response asking four things:
1)
Was I using data on Coors Field that was no longer relevant because the
use of the "humidor room" had diminished the park's offensive edge?
2)
Should the Rockies be allowed
to influence the game this way?
3)
What is it exactly that boosts offense at high altitude?
4)
What is it about the "humidor ball" that is so helpful to pitchers?
For
those who don't know this story, the Rockies for
several seasons now have taken to storing their baseballs in an environmental
chamber that is essentially a large humidor that controls the temperature and
humidity, and yes, it has had a very discernable impact in lessening the
offensive edges experienced at high altitude. In the seasons before the
use of the "humidor room," the number of runs scored per inning
(combination of both teams) was about 59% greater in Colorado home games than road games. In
the seasons since the introduction of the "humidor room" that
figure has been cut by more than half.
To
answer question #1, the data I used referenced only seasons where the Rockies were already using the humidor room,
something they began with the start of 2002, which is two years before the
new park opened in Philadelphia.
Even making minor adjustment to equalize the number of outs used by the home
team and their opponents, Coors Field by an overwhelming margin has been a
better offensive park than Citizens Bank Ballpark.
Runs per
Inning Compared to Road Games
Coors Field Citizens Bank
2004 to
Aug-23-07
+26% +9%
The
Phillies have had the better park for homers in that period, but Coors Field
is the far better park for singles, doubles, triples, and ultimately runs
scored. It is possible that I am still overestimating the modern impact of
Coors Field. The consistency of how the Rockies
have used the environmental chamber is not clear. For example, in 2002 they
set the humidity at 40% but at some point - I believe in 2003 or
part way through 2003 - they raised it to 50% which is the storage
humidity recommended by Rawlings (along with a constant temperature of
70 degrees). In 2006, when there seemed to be a further dip in offense
at Coors Field, a reporter claimed the Rockies
were storing the baseballs for a longer period of time in the humidor room.
But even if you just use the data from 2006-07, which is the closest we can
come to getting these parks near each other, the offensive increase of Coors
Field is 17.6% or exactly double the 8.8% offensive edge of Citizens Bank
Park for those two years.
To
address question #2, it is kind of hard to fault the Rockies
for simply storing baseballs under the conditions recommended by the
manufacturer. In fact, major league baseball is currently adding guidelines
to create greater consistency in the balls being used. The 2007 season is the
first where all 30 clubs will be keeping balls in a temperature controlled
setting, and it is the first season MLB has issued a directive essentially
setting an expiration date on the balls used in games. Only balls purchased
in the current year can be used in a game. Can controlled storage humidity be
far behind?
But
even if the Rockies were being allowed to
doing something slightly different to offset their extreme ballpark effect,
is it really any different a case than allowing them to have the deepest
fences in baseball? We allow a lot of differences within reason and an
acceptable range. We let some teams have artificial turf. We let a lot of
teams have slightly unusual fence depth or configuration, not just the Rockies. We let teams improve their lighting system
above the required standard, and we let them fiddle with their hitting
backgrounds. We let them adjust the thickness and height of their infield
grass. Understand this is not a case of the Rockies
choosing what degree of humidified balls they will play with according to the
opponent. If there were a concern that they were going to cheat that way, it
would be easy enough to safeguard. Simply require the storage room be run and
accessed only by MLB.
Right
now the Rockies are really the only team
that does anything to be sure their balls are within
the range covered by the rulebook. For example, even though there is a rule
that the baseball must weigh between 5.0 to 5.25 ounces, no one other than
the Rockies keeps track of their weight after they leave the factory, even
though we know for a fact that the weight of balls can vary beyond that range
due to something as simple as the level of relative humidity they are stored
in. (An independent study by MLB found in a sample of 3000 balls taken from
storage from ML teams - 100 from each team - that 13% of balls were
underweight, even though they all had passed the weight requirement when
shipped from Costa Rica.)
The
Rockies have found that when stored at the
50% humidity, 70 degree temperatures, recommended by Rawlings that their
balls tend to weigh 5.12 ounces. When the Rockies
examined balls stored before they controlled their environment, they found
some of the balls did not come close to the required range of weight and
circumference. The Rockies had
unknowingly been breaking the rules, and what they are doing now only
brings them back within the rules.
Some
of you may wish to skip over the next few paragraphs as answering questions 3
and 4 are more science than baseball questions. And before you think I am
geekier than I am - which I suppose is considerable - for having so much of
this at the tips of my fingers if not the top of my head, let me explain that
I worked with the Rockies at one point precisely because I was fascinated by
the Mile High effect, and my interest in weather effects on baseball actually
goes all the way back to a thermal environment study that played a key
role in starting my baseball career 26 years ago.
There
are many factors that account for the dramatic impact on offense called the
Mile High effect. Perhaps the most unavoidable relates to a significant
reduction in air resistance. Even with zero wind, air resistance still exists
based on the density of molecules in the air. Technically that air resistance
is a combination of density and viscosity, but we can toss out viscosity
as this varies so slightly there are no meaningful extremes to consider. Air
density, however, can vary quite a bit.
The
three variables influencing air density are humidity, temperature, and air
pressure. Of the three, air humidity - the amount of water vapor in the air -
has the least impact on air resistance. The difference in air density
between, say, the extremes of humidity at 10% and 80% - which is well beyond
the average differences between the most extreme ballparks - is all of 1%.
While it is for the most part insignificant, it is interesting to know the 1%
gain is actually at the HIGHER humidity. All other things being equal, a ball
will carry ever so slightly further in humid air due to lower air density. Water
vapor has an atomic mass of 18 units, and in moist air it is replacing
the heavier molecules of diatomic Oxygen (32 units) and diatomic Nitrogen (28
units), thus resulting in lower air density. The perceived impact of
"heavy" air - humid air – restricting the flight of a baseball has
nothing to do with a change in air resistance. It is the impact
of humidity on the ball itself. That's why the Rockies
humidor room has made a difference. They are putting the balls in the
humidor, not the ballpark.
Temperature
is much more significant than humidity in affecting air density. The hotter
it is, the more molecular motion that is going
on, which expands volume and decreases density. For about every
5-6 degrees difference in temperature (Fahrenheit) there is a 1% difference
in air density. The maximum difference in average temperature during the
baseball season is between Milwaukee
and Miami
with an average difference of 20 degrees. All other things being equal,
air density would average about 3-4% less in Miami than Milwaukee. (All other things aren't
actually equal in this case because Milwaukee
is about 700 feet higher in elevation than Miami. See the next paragraph.)
The
largest influence on air density is air pressure. Even the presence of
a high or low pressure weather system can affect the carry of a
baseball through the air, but altitude generally has a larger impact on air
pressure, and it is variable that is always there. For about every 1000 feet
you are above sea level, air density goes down a little more than 3%. (That
percentage starts to diminish at the extreme elevations but by then you are
also talking about elevations higher than the tallest place on earth.)
By temperature we have an extreme difference in air density between
major league cities of 3-4%, and that is generally the maximum spread for the
influence of altitude if you throw out Denver.
That would leave the tallest major league cities as Phoenix (1100 ft above sea level) and Atlanta (1010 ft above
sea level). But we aren't throwing out Denver,
and air density in Denver
is about 16% less due to reduced air pressure compared to the numerous cities
near sea level in the major leagues.
But
reduced air resistance is not the only intractable element to the Mile High
effect. Changing the air pressure on the sides of the ball is the basis of
all movement of a spinning baseball beyond its forward motion and its
gravitational fall. Every curveball, every slider, the different movement of
the 2-seam and 4-seam fastball, and every variance between a sinking and
sailing fastball - all of it - is tied to air pressure. When you are working
with less air pressure to begin with, the amount of movement resulting from
changing air pressure by spinning the ball would be reduced. Harvard
physicist Robert Adair estimates the reduction in a curveball's movement
is 25% less at Denver's
altitude. Straighter fastballs and less movement on breaking balls is a
real part of the Mile High effect. It's a big reason why Coors Field is
the first ballpark to have a relatively huge impact on strikeout
rates, lowering them to a degree that no other ballpark has ever come close
to matching.
Another
intractable but minor factor of the Mile High effect is a bit of extra
fatigue from not getting enough oxygen during times of exertion. The relative
percentages of the gases in the air are the same at high altitude (oxygen is
21% of the gases in air regardless of the elevation) but with the reduced
pressure there is less of all of the gases in each cubic foot of air, which
means less oxygen is taken in with each breath. Fortunately people can fully
adapt to this even at elevations much higher than Denver's but it isn't instantaneous, and it
isn't helped by moving back and forth between altitudes 5000 feet apart.
But
there is another element to the Mile High effect that is easily controlled,
and surprisingly the tip about its potential magnitude came not from a study
or experiment done by the Rockies but by one commissioned by MLB itself. In
2000 they had the University of Massachusetts-Lowell - which actually has a
"Baseball Research
Center" - study
the difference in distance when hitting the extremes of weight and
circumference allowed for major league baseballs. That is, which would go
farther and how much farther, a 5.25 ounce ball with a 9.25 inch
circumference, or a 5.0 ounce, 9-inch ball. It was not that surprising to
find it was the smaller ball that went further. It had less weight to be
influenced by gravity, and it had less surface area resulting in less air resistance.
They calculated that a home run swing, one that would drive a mid-range ball
(5.125 ounces and 9.125 inches in circumference) 387 feet, would go 421 feet
if it were the smallest legal ball and 372 feet if it was the largest legal
ball. That’s an incredible difference. Two perfectly legal balls could differ
almost FIFTY feet on the same home
run swing. (I suppose that impact is mitigated somewhat in actual practice by
the pitcher being able to throw the smaller ball slightly faster as well.)
High
altitude reduces relative humidity and dew point. In short, it creates
ideal conditions for things to dry out quickly and remain in a state of
dryness. The baseballs in Denver
would get so dry they would lose weight through lost moisture and shrink
a bit. In several cases the lost weight and shrinkage was greater than what
U-Mass was testing. The greatest shrinkage that the Rockies
found in a ball in their old storage room was one that weighed 4.6 ounces and
was 8.5 inches in circumference. The dried out balls were also harder
and slicker, to a point where more than a few pitchers would complain about
not being able to get a good grip on the ball. In fact, the Rockies
said in 2002 that their initial goal in setting up the humidor room was to
improve the grip on the ball.
Better
grip and the balls don't go as far. That's the edge being gained by the
"humidorized" baseballs. It is far from a
perfect solution to the Mile High effect, but it was a big step in bringing
it into a reasonable range, and that is good news for the Rockies
as an organization. When I worked briefly with the Rockies
in the pre-humidor days, I saw a lot of wrong-headed decisions being made
simply because it was so difficult to comprehend a park effect being that
gigantic, and literally everyone had the experience and training to approach
things from the perspective of building a successful club at low altitude.
It wasn’t working, and I don’t think it ever would have worked. They either
had to radically change their thinking and their approach, or they needed to
somehow get the ballpark effect within a range that “low-altitude” mentality
could handle.
Before
the humidor room, Colorado
had a ballpark effect like no other in the history of major league baseball.
It was so far above the norm that the last ballpark to have even half that
type of impact was Philadelphia’s
Baker Bowl way back in the 1929-37 period. Among
ballparks in my lifetime none had even a quarter of the impact of Coors Field
through 2001.
With
the humidor room Colorado
still has an extreme hitter’s park, but at least now it is in the range of
“comprehension.” People can more easily wrap their minds around this type of
park effect, make better decisions. Just as important is that their pitching
is no longer working under the pressure of trying to contain a juiced
offense. That makes it a lot easier to develop a pitching staff with less
volatile swings in health and performance. The biggest effect of the humidor
ball will ultimately be its enhancing the ability of the Rockies
to build a ballclub.
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