Biggest declines from one season to the
next (based on regular season win percentage):
                                          Change in
       Franchise                            win %
  1 Oakland Athletics      1914 -> 1915     -36.8   (65.1  ->  28.3)
  2 Atlanta Braves         1934 -> 1935     -26.9   (51.7  ->  24.8)
  3 Florida Marlins        1997 -> 1998     -23.5   (56.8  ->  33.3)
  4 Cincinnati Reds        1981 -> 1982     -23.4   (61.1  ->  37.7)
  5 Cleveland Indians      1913 -> 1914     -23.3   (56.6  ->  33.3)
  6 Chicago White Sox      1920 -> 1921     -22.9   (63.2  ->  40.3)
  7 Minnesota Twins        1933 -> 1934     -21.7   (65.1  ->  43.4)
  8 Arizona Diamondbacks   2003 -> 2004     -20.4   (51.9  ->  31.5)
  9 San Francisco Giants   1942 -> 1943     -20.0   (55.9  ->  35.9)
 10 Boston Red Sox         1905 -> 1906     -19.5   (51.3  ->  31.8)
 11 Washington Nationals   1994 -> 1995     -19.1   (64.9  ->  45.8)
 12 Chicago White Sox      1917 -> 1918     -18.9   (64.9  ->  46.0)
 13 St. Louis Cardinals    1931 -> 1932     -18.8   (65.6  ->  46.8)
 13 Oakland Athletics      1949 -> 1950     -18.8   (52.6  ->  33.8)
 15 Seattle Mariners       2003 -> 2004     -18.5   (57.4  ->  38.9)
 15 Los Angeles Dodgers    1991 -> 1992     -18.5   (57.4  ->  38.9)
 17 Cincinnati Reds        1944 -> 1945     -18.2   (57.8  ->  39.6)
 18 Detroit Tigers         1988 -> 1989     -17.9   (54.3  ->  36.4)
 19 Detroit Tigers         1919 -> 1920     -17.5   (57.1  ->  39.6)
 20 Oakland Athletics      1992 -> 1993     -17.3   (59.3  ->  42.0)

    Last season:
    Chicago White Sox      2006 -> 2007     -11.2   (55.6  ->  44.4)
    Oakland Athletics      2006 -> 2007     -10.5   (57.4  ->  46.9)
    Minnesota Twins        2006 -> 2007     -10.5   (59.3  ->  48.8)
    New York Mets          2006 -> 2007      -5.6   (59.9  ->  54.3)
    Houston Astros         2006 -> 2007      -5.5   (50.6  ->  45.1)
    Cincinnati Reds        2006 -> 2007      -5.0   (49.4  ->  44.4)
    Florida Marlins        2006 -> 2007      -4.3   (48.1  ->  43.8)
    Detroit Tigers         2006 -> 2007      -4.3   (58.6  ->  54.3)
    Los Angeles Dodgers    2006 -> 2007      -3.7   (54.3  ->  50.6)
    St. Louis Cardinals    2006 -> 2007      -3.5   (51.6  ->  48.1)
    San Francisco Giants   2006 -> 2007      -3.4   (47.2  ->  43.8)
    Texas Rangers          2006 -> 2007      -3.1   (49.4  ->  46.3)
    Toronto Blue Jays      2006 -> 2007      -2.5   (53.7  ->  51.2)
    New York Yankees       2006 -> 2007      -1.9   (59.9  ->  58.0)
    Baltimore Orioles      2006 -> 2007      -0.6   (43.2  ->  42.6)