Unlike those of most sports, baseball playing fields can vary
significantly in size and shape. While the dimensions of the infield are
specifically regulated, the only constraint on outfield size and shape
for professional teams following the rules of Major League and Minor
League Baseball is that fields built or remodeled since June 1, 1958,
must have a minimum distance of 325 feet (99 m) from home plate to the
fences in left and right field and 400 feet (122 m) to center. Major league teams often skirt even this rule. For example, at Minute Maid Park, which became the home of the Houston Astros in 2000, the Crawford Boxes in left field are only 315 feet (96 m) from home plate.
There are no rules at all that address the height of fences or other
structures at the edge of the outfield. The most famously idiosyncratic
outfield boundary is the left-field wall at Boston's Fenway Park, in use since 1912: the Green Monster is 310 feet (94 m) from home plate down the line and 37 feet (11 m) tall.
Similarly, there are no regulations at all concerning the dimensions
of foul territory. Thus a foul fly ball may be entirely out of play in a
park with little space between the foul lines and the stands, but a
foulout in a park with more expansive foul ground.
A fence in foul territory that is close to the outfield line will tend
to direct balls that strike it back toward the fielders, while one that
is farther away may actually prompt more collisions, as outfielders run
full speed to field balls deep in the corner. These variations can make
the difference between a double and a triple or inside-the-park home run.
The surface of the field is also unregulated. While the image to the
left shows a traditional field surfacing arrangement (and the one used
by virtually all MLB teams with naturally surfaced fields), teams are
free to decide what areas will be grassed or bare. Some fields—including several in MLB—use an artificial surface, such as AstroTurf.
Surface variations can have a significant effect on how ground balls
behave and are fielded as well as on baserunning. Similarly, the
presence of a roof (seven major league teams play in stadiums with
permanent or retractable roofs) can greatly affect how fly balls are
played.
While football and soccer players deal with similar variations of field
surface and stadium covering, the size and shape of their fields are
much more standardized. The area out-of-bounds on a football or soccer
field does not affect play the way foul territory in baseball does, so
variations in that regard are largely insignificant.
These physical variations create a distinctive set of playing conditions at each ballpark. Other local factors, such as altitude and climate, can also significantly affect play. A given stadium may acquire a reputation as a pitcher's park or a hitter's park, if one or the other discipline notably benefits from its unique mix of elements. The most exceptional park in this regard is Coors Field, home of the Colorado Rockies. Its high altitude—5,282 feet (1,610 m) above sea level—is responsible for giving it the strongest hitter's park effect in the major leagues. Wrigley Field, home of the Chicago Cubs, is known for its fickle disposition: a hitter's park when the strong winds off Lake Michigan are blowing out, it becomes more of a pitcher's park when they are blowing in. The absence of a standardized field affects not only how particular games play out, but the nature of team rosters and players' statistical records. For example, hitting a fly ball 330 feet (100 m) into right field might result in an easy catch on the warning track at one park, and a home run at another. A team that plays in a park with a relatively short right field, such as the New York Yankees, will tend to stock its roster with left-handed pull hitters, who can best exploit it. On the individual level, a player who spends most of his career with a team that plays in a hitter's park will gain an advantage in batting statistics over time—even more so if his talents are especially suited to the park.
These physical variations create a distinctive set of playing conditions at each ballpark. Other local factors, such as altitude and climate, can also significantly affect play. A given stadium may acquire a reputation as a pitcher's park or a hitter's park, if one or the other discipline notably benefits from its unique mix of elements. The most exceptional park in this regard is Coors Field, home of the Colorado Rockies. Its high altitude—5,282 feet (1,610 m) above sea level—is responsible for giving it the strongest hitter's park effect in the major leagues. Wrigley Field, home of the Chicago Cubs, is known for its fickle disposition: a hitter's park when the strong winds off Lake Michigan are blowing out, it becomes more of a pitcher's park when they are blowing in. The absence of a standardized field affects not only how particular games play out, but the nature of team rosters and players' statistical records. For example, hitting a fly ball 330 feet (100 m) into right field might result in an easy catch on the warning track at one park, and a home run at another. A team that plays in a park with a relatively short right field, such as the New York Yankees, will tend to stock its roster with left-handed pull hitters, who can best exploit it. On the individual level, a player who spends most of his career with a team that plays in a hitter's park will gain an advantage in batting statistics over time—even more so if his talents are especially suited to the park.