In sports, park effects are the unique factors of each stadium or arena that impact a game's outcome. These effects are broken down into different components and used in advanced statistical analysis. While most sports have regulation-sized fields, some sports or leagues, such as Major League Baseball (MLB) and NCAA hockey, allow for varying field of play dimensions. The most common example of a park effect is a baseball stadium's batting park factor, but there exist other factors that impact all sports. Every stadium throughout the world has its own unique effects that impact the sports played there.
Park factors (baseball) Because baseball allows for unique field dimensions, each stadium is prone to favoring certain outcomes, and thus can favor pitchers or hitters. This has become the most prominent park effect, known as park factors (PF), which indicate the difference between a team's offense and defense in home and road games. These calculations generally exclude Coors Field, due to its higher altitude, and interleague games, due to the variation of the designated hitter (DH) until the 2020 season, when the DH position was added by the National League. Used as a part of many statistical prediction models, park factors can explain varying offensive outputs of specific players, teams and eras of baseball. These factors can be produced based on many offensive statistics, but are generally and most easily calculated based on team runs and home runs.
Calculations A general description of park factors includes comparing the number of runs scored and allowed by each individual team at home and subsequently compared to league average. League average can be adjusted for each team to account for which stadiums each team actually played in, but statistically, the difference is marginal and is thus ignored. Runs scored are compared to games (or outs, as there are 27 outs in a game) rather than plate appearances, because the outs per game stay constant while the number of plate appearances changes. The following formulas calculate park factors:
P F = H T ( T − 1 ) ( R + H ) {\displaystyle \mathrm {PF} ={\frac {HT}{(T-1)(R+H)}}}
where H {\displaystyle H} is the number of home runs per game, R {\displaystyle R} is the number of road runs per game, and T {\displaystyle T} is the number of teams in the league. The intermediate park factor (iPF) makes PF applicable to composite stats rather than just home stats. iPF is calculated as follows:
i P F = P F + 1 2 {\displaystyle \mathrm {iPF} ={\frac {\mathrm {PF} +1}{2}}}
The final PF (fPF) uses weights to regress the data based on which year it came from. Although weights can be calculated in various ways, the general consensus is any differences are marginal. fPF is calculated as follows:
f P F = 1 − ( 1 − i P F ) X i {\displaystyle \mathrm {fPF} =1-(1-\mathrm {iPF} )X_{i}}
where X i {\displaystyle X_{i}} is the weight for the i {\displaystyle i} th year. These calculations give fPF on a scale of 1, meaning that 1 is the league average and every hundredth (0.01) above or below 1 corresponds to one percent above or below the league average. For example, an fPF of 1.20 means that offense, based on runs, is expected to be 20% increased; and, vice versa, a fPF of 0.80 means that offense is expected to be decreased by 20%.
Application outside Major League Baseball Park factors have recently been applied to leagues outside the MLB. In Minor League Baseball, there are 160 affiliate teams above the rookie complex level, across 14 leagues, of which all have their own park factors, determined by various offensive stats, the most common being runs and home runs. Further examples include the calculation of park factors in Nippon Professional Baseball and prospective future calculations by FanGraphs in the Korea Baseball Organization. Park factors have even been calculated for non-professional leagues, such as the Cape Cod League, a top summer collegiate baseball league in the United States.
Altitude Altitude affects all sports in various ways. At higher altitudes, all physical activity becomes more difficult for many reasons, including the lower oxygen levels. But beyond the impact on the athletes, who experience physiological effects in all sports, higher altitudes also result in less air resistance on moving objects. In baseball, this lower air resistance produces more runs. While much of the research regarding the effects of altitude on the flight of baseballs is relative to more home runs, altitude has been shown to increase offense in all aspects which contact is made. The only MLB stadium of significantly high altitude is Coors Field; however, there are several other professional stadiums throughout the country also at high altitudes. MLB stadium altitudes range from the 5,211 feet (1,588 m) above sea level of Coors Field to the 20 feet (6.1 m) of Philadelphia's Citizen Bank Park. Yet, one must consider that much of the influence of altitudes is de facto calculated in a stadium's park factor as a result of total offensive output by stadium.
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