ABSTRACT
The Effect of Meteorological
Conditions on Fly Ball
Distances in North American
Major League Baseball
Games
Mark D. Kraft
Professor
Brent R. Skeeter
Professor
This study examines the effect of meteorological conditions on the flight of
baseballs hit in North American major
league baseball games. Statistical analyses are used to relate game-time tem perature, humidity, wind speed and wind
direction data to the flight distance of
every fair fly ball hit in non-domed stadiums during the 1991 and 1992 seasons. Results indicate that temperature
is the most important meteorological
variable affecting fly ball distances at
most stadiums. The effect of wind speed
and direction varies in different stadi ums, with surprising influences at certain stadiums. The results of this study
may be strategically valuable to managers and coaches searching for any
possible edge to win a game.
KEY WORDS : baseball , domed stadium, fly
ball distance, meteorological conditions,
sport
INTRODUCTION
Department of Geography and Regional
Planning
Salisbury State University
Salisbury, MD 21801
40
Every season professional baseball
teams are faced with many decisions
during the course of their games that influence their likelihood of winning. It is
the job of the coaching staff to make
those decisions. If they make the correct
ones, their chances of winning will increase. In order to increase the chance
of making the correct decisions, the
coaching staff should attempt to obtain
all potentially significant information. For
example, they would want to know individual player abil ity, such as a hitter's
success against left-handed pitching or
right-handed pitching, or more specifically, against a particular pitcher. It may
be helpful to know a hitter's or pitcher's
performance in night games compared
to day games, or their performance
against a particular team . There are many
more possibilities that a coaching staff
needs to consider, all of which are vital
to a team's success.
Although perhaps not at first obvious, the coaching staff may also want
to know such meteorological information as wind speed, wind direction, temperature and humidity because of its
possible influence on how the ball travels. In the case of temperature, cold air
is more dense than warm air. Given this
fact, with all else being equal, a freely
moving object will travel farther in warm
air, which is less dense, then it will in
cold , more dense air. In baseball terms,
with all else being equal, a fly ball should
travel farther on a warm day than on a
cold one. In a game situation, again with
all else being equal, on a warm day or
evening, the decision to bring in a pitcher
who tends to throw high in the strike
zone would seem to be illogical because
that type of pitcher will typically give up
more fly balls. In this case the warm
weather may result in an increase in the
number of home runs and / or the number of balls which are hit beyond the
outfielder's reach.
With the variable of humidity, or the
amount of moisture in the air, humid air
is less dense than dry air. This is the opposite of what most people think since
humid air "feels thick". Water vapor is
only about 64 percent as dense as dry
air. Therefore, as the water vapor content of the air increases, the air density
decreases accordingly. Thus, a fly ball
will travel farther in the less dense, more
humid air. In a game situation, a fly ball
should have a greater chance of becoming a home run or being hit beyond the
outfielders on a humid day.
In the case of wind speed and wind
direction, it would certainly seem that
strong winds blowing out of the ballpark
should increase fly ball distances with
the reverse being true for winds blowing
in. If the manager and his coaching staff
are aware these meteorological variables have an effect on baseball games,
then the utilization of meteorological information may improve the success of
the team as a whole.
To date, studies examining the effect
of weather conditions on the flight of
baseballs in actual games have relied
solely on the number of home runs hit
during different meteorological conditions (eg., Kingsley, 1980). It is preferable, however, to be able to analyze more
than just variations in the number of
home runs which are hit. Specifically,
what is most useful is to be able to ex-
amine variations in the distances of all
fly balls put into play in major league
games. The objective of this research is
to examine the influence of meteorological variables on fly ball distance in major league baseball games.
METHODOLOGY
The data used in this study are from
a total compilation of every game played
in both the American and National Leagues for the years of 1991 and 1992, totaling over 4000 games. The locations of
the 26 North American major league
teams playing in 1991 and 1992 are
shown in Figure 1. The data were obtained from STATS, Inc. Among the
wealth of information that STATS, Inc.
records for every major league game are
the game time temperature, relative hu midity, wind speed, wind direction and
the estimated distance of travel of every
ball put into play. Only fly ball distances
were examined in this research because
their distance of travel is most affected
by meteorological conditions.
Each game has had the distances of
each fly ball averaged to obtain a game
average distance (Table 1). Even though
these are the most complete data available for completing research of this nature (in fact, they are the only source of
fly ball distances for all major league
games), there are some limitations. For
example, meteorological recordings are
made at each game's starting time. During the course of a game, which averages approximately three hours, those
conditions can change. Also, there were
several games for which relative humidity was not recorded. These games were
eliminated from the data set. In addition,
relative humidity was never recorded for
any of the games played in domed stadiums. Therefore, games played in
domed stadiums were also not used in
the analyses. In the cases of Toronto and
Montreal, which have retractable domes,
only those games played when the roof
was open were included. Because all of
the recorded fly ball distances were estimates, the precise fly ball distances are
actually unknown. However, because the
data set is so large (including over 50,000
fly balls), we feel confident that we can
41
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13. Chicago
14. Detroit
15. Cincinnati
16. Atlanta
17. Cleveland
18. Toronto
19. Pittsburgh
20. Baltimore
21 . Philadelphia
22. New York (2)
23. Boston
24. Montreal
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11 . Minneapolis
12. Milwaukee
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FIGURE 1. Location of the 24 North American cities having major league baseball
teams in 1992. Chicago and New York have two teams each . D indicates a domed
stad ium and R indicates a retractable domed stad ium . (Denver, Colorado and Miami,
Florida were added as major league cities in 1993.)
rely on the distances obtained since in dividual errors (i.e., over- or under-estimations) should cancel out one another.
Tempe rature
Temperat ure was broken up for analys is using two methods. The first was to
analyze all games played with a temperature below 70°F and then all games
70°F and warmer. An actual average fly
ball distance was then calculated for each
of the two categories.
The second method was to break the
games up into ten degree increments in
the following manner: < 50°F, 50-59°F,
60-69°F, 70-79°F, 80- 89°F and 90°F and
warmer. Again, an average fly ball distance was obta ined for each category_
42
Wind
For the variable of wind , the data had
to be altered _ If the wind direction was
recorded as blowing out to left field, out
to center field or out to right field, no
changes were made to the velocity value.
If w ind direction was recorded as blowing from left field to right f ield or from
right field to left field , a velocity value of
o was given because it should have little
if any effect on the distance of the fly
ball _ If wind direction was recorded as
blowing in from any field towards home
plate t he velocity was assigned a negative value_ For example. a velocity of 12
mph. blowing in from left field would be
given a value of - 12 mph_
Wind was also preliminarily exam-
TABLE 1
Sample Fly Ball Data (ft) Major Leagues 1992
Vis
Home
Cle
Tor
Mil
Cle
Sea
Mon
LA
Bal
Bos
Cal
Cal
Cle
Atl
SD
Hou
Cin
SF
LA
Date
Temp
Humid
Dir
Vel
#
Dis
Avg
Aws
04/ 06 / 92
04/ 17/ 92
04/24/ 92
08/ 31 / 92
06/ 02 / 92
05/ 17/ 92
06/ 22 / 92
09 / 27 / 92
09/ 26/ 92
63
40
72
73
64
80
78
82
87
40%
90%
65%
60%
40%
80%
63%
40%
10%
4
6
2
4
4
8
4
2
8
12
13
5
5
5
12
7
10
1
15
10
13
20
10
16
9
9
23
4540
2870
3840
6120
3330
5360
2890
2720
6920
302
287
295
306
333
335
321
302
300
0
- 13
5
0
0
0
0
10
0
Where :
VIS-Visiting team
HOM-Home team
TEMP-Temperature (P) at game time
HUMID-Relative humidity at game time
DIR-Wind direction (1-out to left, 2-out to center, 3-out to right, 4-left to right, 5-in from left,
6-in from center, 7-in from right, 8-right to left)
VEL-Wind velocity in miles / hour
#-Number of fly balls
DIS-Total distance of all fly balls hit in the game in feet
AVG-Average fly ball distance in feet
AWS-Altered wind speed in miles/hour
ined using the method of breaking the
data into categories and obtaining a fly
ball average for each. The categories are
as follows : wind blowing out. wind
blowing across, and wind blowing in.
Statistical Analysis
Once the fly ball averages were obtained it was necessary to analyze them
statistically to determine any significant
differences in the distances. Nonparametric tests were used because the data
did not meet the more stringent assumptions for the use of parametric tests
(McGrew and Monroe, 1993). The first
statistical test used was the Wilcoxon
rank sum W test. This test is useful for
comparing differences between two
samples and was used to compare fly
ball distance differences for the temperature categories of below 70°F and at
least 70°F.
In order to analyze the differences in
the data for 10 degree increments of
temperature and for the wind categories, a different non parametric test had
to be used because there were more than
two categories . In these two cases a
Kruskal -Wallis one-way analysis of variance test was utilized . This test can be
considered to be the non parametric extension of the Wilcoxon rank sum W test
for situations with more than two sam ples (McGrew and Monroe, 1993).
Regression analysis was used to determine the percentage of the variability
in the fly ball distances accounted for by
the meteorological variables. Temperature, wind speed and direction, relative
humidity and altitude were analyzed individually using linear regression and all
of the variables were analyzed together
using multiple regression.
In addition, a test study of air pressure was run using regression. The cities of New York and Seattle were used
in this study. New York was chosen because the weather patterns of the northeastern United States are effected greatly
by mid-latitude cyclones, thereby altering the air pressure frequently. Seattle
was chosen because the altitude of that
city is similar to New York's and the
Mariners play in a dome. A dome was
43
h
TABLE 2
Average Fly Ball Distance
(ft) «, >= 70°F) Major
Leagues 1991-1992
Temperature
Range (OF)
Average Fly Ball
Distance (tt)
<70
>=70
308
313
chosen because that eliminates all other
meteorological variables with air pressure remaining as the only variable because the other conditions are kept
constant.
Finally, there has been considerable
speculation among players and in the
Toronto media that fly balls travel differently during games when the Toronto
dome is closed versus when it is open.
Specifically, it has been suggested that
the ball travels farther when the dome
is closed. Therefore, the average fly ball
distance for all open and closed domed
games in Toronto was also computed.
RESULTS
The average fly ball distances for the
above and below 70°F cases are similar
to what one would probably expect (Table 2).
It is especially interesting to note the
extremes when the games are broken
down into 10 degree temperature increments (Table 3). The average fly ball dis-
TABLE 3
Average Fly Ball Distance
(ft) (10°F Increments)
Major Leagues
1991-1992
Temperature
Range (OF)
Average Flyball
Distance (tt)
< 50
50-59
60-69
70-79
80-89
> =90
304
309
308
311
314
320
44
TABLE 4
Average Fly Ball Distance
(ft) (Wind Direction)
Major Leagues
1991-1992
Wind
Direction
Blowing In
Blowing Across
Blowing Out
Average Flyball
Distance (tt)
311
311
312
tance for games played in temperatures
below 50°F is 16 feet less than for those
played when the temperature was at least
90°F. The results of these preliminary
analyses show that there was a difference in fly ball distance with temperature.
The findings with wind showed
something completely different. With
wind broken up into the three categories
of blowing in, out or across and looking
at every game, there are some rather
striking results (Table 4).
There is an almost nonexistent difference in fly ball distance no matter what
direction the wind is blowing . It must be
emphasized that these results are contrary to what most people would generally assume to be correct. This is due
to the fact that these results are based
on the regional scale winds values. The
smaller scale windflow patterns resulting from the microclimatic effects of the
individ ual stadiums apparently often
dominate over the regional scale flow.
There are numerous stadiums where the
flags show the wind to be blowing out
when in fact it effects a baseball as it was
blowing in. A prime example of this situation would be Oriole Park at Camden
Yards in Baltimore. The Orioles started
play in this park in 1992, therefore, the
data for 1991 occurred in Memorial Stadium which had vastly different characteristics then Oriole Park. When Oriole
Park was built in 1992, it was assumed
by its designers and baseball experts that
the ball would fly out of this park, especially in right field with its short dimensions and "tall wall" . However, one
of the qualities of this park is the large
TABLE 5
Wilcoxon Rank Sum W
Test Major Leagues
TABLE 6
Kruskal-Wallis One-way
Analysis Of Variance Six
Temperature Categories
Major Leagues
1991-1992
Temperature
(OF)
<>70
w
z
p-value
1505624.0
- 8.30
.0000
warehouse just beyond the right field
wall. The presence of this building causes
the wind that is blowing out to deflect
off the warehouse and actually blow towards home plate (Bosman, 1992). This
case is not unusual and can be found in
numerous ballparks, especially those that
are enclosed such as Veterans Stadium
in Philadelphia. So when it is recorded
that the wind is blowing out, in fact, in
many parks it is blowing in, resulting in
the lack of difference in fly ball distance
for the major leagues. The effect of winds
at specific individual ballparks is addressed in more detail later in this paper.
To determine the statistical significance of the differences in the 70 degree
split, the Wilcoxon rank sum W test was
performed. The results for the major
leagues reveal that there is a statistically
significant difference in fly ball distance
with a significance level of .0000 (Table
5). Therefore one can conclude, with near
100 percent certainty that with all else
being equal fly balls travel shorter distances when the temperature is below
70°F than when the temperature is 70°F
or warmer.
When the games were broken into six
temperature categories a Kruskal-Wallis
one-way analysis of variance test was
performed. Again, with a significance
level of .0000 (Table 6)' one can conclude that the fly ball distances increase
significantly when temperatures increase.
The results of the various regression
tests produced some interesting results.
The first tests of linear regression were
perfo rmed on temperature, wind speed
and direction, humidity and altitude (Table 7).
The most interesting result of the linear regression involves wind, with the
1991-1992
Chi-Square
p-value
129.65
.0000
numbers reverting back to the previous
tests, showing no significance, thus
backing up those preliminary results.
With wind having such a low r2 and high
p-value level it shows that for the major
leagues as a whole the regional scale
wind has no significant effect on fly ball
distance. The only two variables that have
any significant effect are temperature and
altitude. Even though the amount of
variance that they account for is minimal, they are significant.
The pilot study using the New York
Yankees and Seattle Mariners concluded
that air pressure has no significant effect
on fly ball distances (Table 7). In both
cases air pressure was not significant at
the .10 level.
In the case of the multiple regression
test for the major leagues, the combination of all of the variables were significant with a .0000 p-value and an R2
of .062 (Table 8), meaning that the meteorological variables are responsible for
6.2 percent of the difference in fly ball
distances during the major league games.
The variable having the least influence on fly ball distances was relative
humidity. Kingsley (1980) found this same
result using home run frequencies. This
may simply be because relative humidity is a poor measure of the actual moisture content of the air because it is temperature dependent. A preliminary
examination using the Temperature-Humidity Index (which takes temperature
and relative humidity into account together) showed that also to be insignificant. It appears most likely that the variations in air density associated solely
with changes in the air's moisture con-
45
TABLE 7
Linear Regression Major Leagues 1991-1992
p-value
Variable
.03655
.02891
.00046
.00039
.01367 /. 00748
Temperature
Altitude
Wind Velocity
Relative Humidity
* Air Pressure
.0000
.0000
.2213
.2596
.1409/.2738
* variable analyzed in pilot study-complete Major League results unknown (New York/Seattle)
TABLE 8
Multiple Regression
Major Leagues
1991-1992
p-value
.062
.0000
tent are simply too minor to have any
significant effect on fly ball distances.
Wind was found to be significant in
the multiple regression even though it
was found to be insignificant in the linear regression model. This may be due
to the fact that for the league as a whole,
there is no difference in fly ball distance
when the wind is blowing in versus
blowing out. However, as wind varies,
fly ball distances vary at individual
ballparks.
Individual Teams
Although the major leagues as a
whole have so far been the subject of
analysis, individual teams were also
looked at to determine what differences
exist between ballparks. One of the more
striking findings is that in some ballparks fly ball distance decreases as the
season progresses with more games
being played in days when the temperature is above 70°F (Table 9).
This is true in Baltimore, Milwaukee
and for the Chicago Cubs. When the
temperature is above 70, there tends to
be a southwesterly flow and with most
stadiums being oriented toward the
northeast (Skeeter, 1988), winds should
blowout. However, in Chicago and Mil-
46
TABLE 9
Average Fly Ball
Distances (tt) «, > =
70°F) Individual Ballparks
1991-1992
City/Team
Baltimore
Milwaukee
Chicago Cubs
315
312
310
312
310
308
waukee the breeze off of Lake Michigan
that is created on these warm days
causes the winds to blow in with a
greater frequency during warm periods.
In the case of Baltimore, as was previously explained, when the regional scale
winds are from the southwest the warehouse often causes the wind to reverse
and blow in (Table 10).
Again, there are other cities in addition to Baltimore where fly ball distance
is shorter when the wind is blowing out.
This is true for Baltimore, Philadelphia,
St. Louis and Toronto (Table 10). Incidentally, in Los Angeles and San Diego
the wind never blew in during any of the
games (Table 10). Tables 11-13 list the
cities which were found to have statistically significant results (p-value < .05)
for each category.
The most noticeable aspect of Tables
11-13 is that Boston appears on each
one. From this it appears that games
played at Boston are affected most by
meteorological variables.
Finally, for 1991-92 there were 80 Toronto home games played with the dome
closed and 82 played with the dome
TABLE 10
Average Fly Ball Distances (tt) (Wind Direction) Individual Ballparks
1991-1992
City
Baltimore
Ph iladelphia
St. Louis
Toronto
Los Angeles
San Diego
Blowing
In
Blowing
Across
Blowing
Out
314
312
321
315
314
312
319
321
312
305
311
311
319
305
310
305
N/ A
N/ A
TABLE 11
Significant Difference In
Fly Ball Distance
«, >= 70°F)
TABLE 13
Multiple Regression
Individual Teams
1991-1992
p-value
City/ Team
Boston
San Diego
Pittsburgh
Chicago White Sox
.0019
.0061
.0139
.0426
open. The average fly ball distance for
the closed-dome games was 314 feet. For
the open-dome games the average was
313 feet. Therefore, at least based on
these two years, it appears that closing
or opening the dome has virtually no effect on fly ball distances.
CONCLUSIONS
The results of this study show, perhaps surprisingly, that temperature is the
most important meteorological variable
affecting fly ball distances for the major
TABLE 12
Significant Difference In
Fly Ball Distance
(10°F Increments)
City
Boston
San Francisco
Baltimore
p-value
.0169
.0441
.0489
City/Team
Milwaukee
San Diego
Boston
Ch icago Cubs
Chicago W.S.
Kansas City
~
p-value
.105
.067
.099
.073
.062
.051
.0006
.0119
.0133
.0247
.0310
.0418
leagues as a whole. Wind is not particularly important for the leagues overall.
However, in certain ballparks wind does
have a major influence on fly ball
distances.
Temperature, being the most important variable should possibly be given
strategic consideration during individual
games. In order to harness an advantage based on the wind, the individual
ballpark must be taken into consideration since the effect of wind is unique
to each site. Altitude was also significant
even though the highest city in the major leagues (prior to 1993) was Atlanta,
Georgia . Relative humidity and air pressure have been found to be insignificant, although the latter was not completely analyzed .
It is also important to recognize that
Boston was the only city to appear in all
statistical analyses as being significant.
It may be concluded that Boston is the
47
only major league city where fly ball distances are affected significantly by all of
the meteorological variables analyzed.
Incidentally, there has also been some
controversy in Boston as to whether the
addition of the sky boxes has cut down
on the number of fly balls hit because
of the alteration of the airflow in Fenway
Park.
Additional research on this topic might
include adding the 1993 and 1994 results, especially with the addition of the
Colorado Rockies in Denver and the
Florida Marlins in Miami . Analysis of the
Colorado data would be particularly useful for helping to determine the effect of
altitude on fly ball distances. Much more
detailed studies (including microclimatological analyses) could be performed
48
for each stadium with an extensive analysis on how each variable affects the fly
balls in that stadium.
REFERENCES CITED
Bosman, Dick. (Baltimore Orioles Pitching
Coach) . 1992. Personal Communication .
Kingsley, R. H. 1980. Lots of Home Runs in
Atlanta? Baseball Research Journal, 2: 6671.
McGrew, J. C. and C. B. Monroe, 1993. Statistical Problem Solving in Geography, Wm .
C. Brown. Dubuque, IA
Skeeter, B. R., 1988. Winds and the Baseball
Stadium : General Wind Characteristics in
Major League Baseball Stadiums. Sport
Place International. 2 (1) : 37-44.
STATS Inc. (Sports Team Analysis & Tracking
Systems, Inc.) 1991-1992. Lincolnwood, IL.