Major League Baseball's geographic line-up essentially was constant between 1903 and 1953, when the Boston Braves moved to Milwaukee and the new publicly financed stadium built on their behalf. Other MLB teams moved prior to the 1954, 1955, 1958, 1961, 1968, 1970, 1972, and 2005 seasons. In addition to team relocation, MLB has added new teams several times since 1950. The first expansion occurred in 1961, in response to the threat of a proposed third league, with the addition of the Los Angeles Angels and a new incarnation of the Washington Senators. Subsequent MLB expansion occurred in 1962, 1969, 1977, 1993 and 1998. What had been sixteen-team league in 1960 grew to thirty franchises by 2006, an increase of 87.5%. While there has been relatively little academic study of the effects of team relocation, "conventional wisdom" holds that MLB league expansion leads to distribution of the available baseball talent across more teams, and that the thinning of talent has a greater negative effect on quality of pitching than on hitting. Furthermore, it is widely believed that competitive balance is reduced for at least the first year following expansion. This paper analyzes the effects of MLB expansion and team relocation between 1950 and 2004 on trends in game attendance, within-season competitive balance, and the balance between offense and defense. This is done by testing a series of time-series "shock" models on a comprehensive statistical data set assembled from The Baseball Archive and number of other sources. The models consider the effects of relocation and expansion shocks of differing relative magnitudes, while controlling for changes in MLB's population coverage, the effects of new stadia, and the consequences of labor strife. Taking these controls into account, team relocation was found to have a depressing effect on the trend of increasing average MLB attendance per home date during 1950-2004, but not on competitive balance, or on the balance between offense and defense. League expansion was found to have no net effect on trends in average MLB home date attendance, or the balance between offense and defense. However, expansion was found to depress growth in home date attendance for incumbent (i.e., non-expansion) teams, to reduce competitive balance, and to set back the trend of increasing of average team fielding percentage. The reduction in competitive balance in expansion years was found to hold across all teams, as well as among incumbent teams only.
