Stadium Boom Amounts to Fountain of Youth for MLB Parks

When conducting baseball research, my thoughts often turn to the state of the baseball economy and the effect of new ballparks on the game. However, I've personally never seen the new stadium boom quantified—let alone visualized—so I decided to take a swing at it. Here's what I came up with.


By plotting the age of all MLB parks across time, it becomes very apparent when baseball construction was booming. We see two very clear eras of stadium growth: first, with the expansion years of 1961-1977, and second, with the stadium boom of the 1990s onward.

While this was the general pattern I expected, I was somewhat surprised to see that the average ballpark is just as young today as it was immediately following expansion, although the rejuvenation of MLB parks does seem to be more durable this time around.

Notable Facts and Figures:

  • In 1960, the final season before expansion, the average MLB ballpark was 37.3 years old. In 1977, the final season of the expansion wave, the average age sat at just 20.8 years: a drop of 16.5 years of age—nearly one year per season.
  • The single most "rejuvenating" year for MLB parks was not an expansion year at all. In 2000, the average age declined from 27.3 to 22.8 years: a drop of 4.5. Leading scientists credit this anti-aging miracle to the Tigers, Astros and Giants all moving into brand new parks. Their previous grounds averaged 53.7 years since their first opening day, led by Tiger Stadium at the ripe old age of 87.
  • The next greatest one-year drops occurred in 1971 (-4.0 years) and 1961 (-3.8). The former was the result of the Phillies and Reds moving into newer facilities. The latter was accomplished by the relocation of the original Washington franchise to the HHH Metrodome Metropolitan Stadium in Minneapolis, along with the advent of the Houston Colt .45s and the brand new, state of the art facility we all know as Colt Stadium.
  • MLB parks averaged their oldest in 1952 at 38.9 years old. In 1974, they averaged only 20.1 years old, the youngest mark of the modern era. Parks would continue to age steadily up until the 1990 post-expansion high of 31.8 years. The stadium boom that followed lowered their average age to a post-expansion low of 20.8 in 2004.
  • There were, in fact, two seasons when the average age increased by more than a single year. The most obvious is 2005, when the Montreal Expos moved out of 27-year-old Le Stade Olympique and into the 46-year-old Robert F. Kennedy Stadium (in their new incarnation as the Washington Nationals). The other season is less obvious: in 1955, the Philadelphia Athletics left for Kansas City, trading a 42-year old stadium for a slightly newer 32-year old model. This actually increased the mean, however, as the calculation now included two middle-aged stadia—one 32 years old and one 43—instead of just one.

    There are three choices I made regarding the data that are worth addressing. First, I treated major renovations differently than minor ones. When a stadium is torn to the ground and rebuilt, a la Yankee Stadium 1974-75 (or less notably, Memorial Stadium in Baltimore 1949-50), I count the renovated park as a new park with a new opening date. For more common renovations, such as the recent makeovers of Fenway and Kansas City's Kauffman Stadium, I went with the original open date.

    Second, when two teams shared a stadium (as with the St. Louis Cardinals and Browns through 1953) I counted the park only once.

    Finally, alternate home sites, such as the Expos games in Hiram Bithorn Stadium in San Juan, PR, or the exhibition games that the Chicago White Sox played in Milwaukee following the departure of the Braves, did not figure into the data.

    The data for the chart are presented below. A larger picture of the chart is available upon request, as I prefer to handle the shrinking of my images rather than leave it up to SB Nation's CMS. All data were obtained via Wikipedia.

    Average Age of MLB Ballparks, 1920-2010
    Year Mean Age Year Mean Age Year Mean Age
    1920 10.8 1930 20.0 1940 28.4
    1921 11.8 1931 21.0 1941 29.4
    1922 12.8 1932 22.0 1942 30.4
    1923 13.0 1933 23.0 1943 31.4
    1924 14.0 1934 24.0 1944 32.4
    1925 15.0 1935 25.0 1945 33.4
    1926 16.0 1936 26.0 1946 34.4
    1927 17.0 1937 27.0 1947 33.9
    1928 18.0 1938 28.0 1948 34.9
    1929 19.0 1939 27.4 1949 35.9
    Year Mean Age Year Mean Age Year Mean Age
    1950 36.9 1960 37.3 1970 24.7
    1951 37.9 1961 33.5 1971 20.7
    1952 38.9 1962 31.9 1972 21.5
    1953 37.1 1963 32.9 1973 20.4
    1954 34.7 1964 31.0 1974 20.1
    1955 36.6 1965 32.0 1975 21.1
    1956 37.6 1966 30.7 1976 21.2
    1957 38.6 1967 28.5 1977 20.8
    1958 37.0 1968 27.3 1978 21.8
    1959 38.0 1969 26.9 1979 22.8
    Year Mean Age Year Mean Age Year Mean Age
    1980 23.8 1990 31.8 2000 22.8
    1981 24.8 1991 29.7 2001 21.2
    1982 24.8 1992 29.0 2002 22.2
    1983 25.8 1993 29.7 2003 22.1
    1984 26.8 1994 27.4 2004 20.8
    1985 27.8 1995 26.8 2005 22.4
    1986 28.8 1996 27.8 2006 22.1
    1987 29.8 1997 27.7 2007 23.1
    1988 30.8 1998 27.0 2008 22.4
    1989 30.8 1999 27.3 2009 20.8
    2010 20.9
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