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Thursday, January 24, 2013

Two teams, one park, different park factors.

From 1903 through 1975 two teams (one AL, one NL) have shared the same ball park in a season 65 times.  None since then.  Only the two seasons (1974-1975) the Yankees and Mets shared Shea Stadium did the AL team use the designated hitter (DH).

In New York the Yankees and Giants shared the Polo Grounds 1913-1922.

In St. Louis Cardinals and Browns shared Sportsman's Park 1921-1953.  Then the Browns morphed into beautiful birds, the Baltimore Orioles.

In Philadelphia Athletics and Phillies (Blue Jays some seasons) shared Shibe Park 1939-1954.  In 1955 the Athletics moved to Kansas City.  Shibe Park was renamed Connie Mack Stadium 1953-1976 after the Athletics owner.

In Los Angeles Dodgers and Angels shared Dodger Stadium 1962-1965.

So how come the park factor is different for one team almost every season?  Because baseball is played in non-uniform playing areas a park factor is needed to try to equate stats.  There are actually two park factors, one for batters (BPF), one for pitchers (PPF).

BBF is equal in only 11 of the 65 shared seasons:



yearID park TeamAL TeamNL BPFal
1921 Polo Grounds IV New York Yankees New York Giants 102
1922 Polo Grounds IV New York Yankees New York Giants 102
1928 Sportsman's Park IV St. Louis Browns St. Louis Cardinals 103
1933 Sportsman's Park IV St. Louis Browns St. Louis Cardinals 106
1934 Sportsman's Park IV St. Louis Browns St. Louis Cardinals 107
1935 Sportsman's Park IV St. Louis Browns St. Louis Cardinals 104
1949 Shibe Park Philadelphia Athletics Philadelphia Phillies 97
1950 Shibe Park Philadelphia Athletics Philadelphia Phillies 98
1950 Sportsman's Park IV St. Louis Browns St. Louis Cardinals 104
1954 Connie Mack Stadium Philadelphia Athletics Philadelphia Phillies 100
1974 Shea Stadium New York Yankees New York Mets 99


In St. Louis when the teams had the same BPF three consecutive years it was different each year: 106, 107, 104.  Same thing in Philadelphia for two consecutive years: 97, 98.  Oddly the Yanks with the DH and Mets are one of the 11 seasons when the teams had the same BPF.

PPF same:


yearIDparkTeamALTeamNLPPFnl
1921Polo Grounds IVNew York YankeesNew York Giants98
1922Polo Grounds IVNew York YankeesNew York Giants98
1938Sportsman's Park IVSt. Louis BrownsSt. Louis Cardinals104
1939Sportsman's Park IVSt. Louis BrownsSt. Louis Cardinals105
1940Shibe ParkPhiladelphia AthleticsPhiladelphia Phillies101
1941Shibe ParkPhiladelphia AthleticsPhiladelphia Phillies101
1941Sportsman's Park IVSt. Louis BrownsSt. Louis Cardinals104
1946Shibe ParkPhiladelphia AthleticsPhiladelphia Phillies100

Two instances when both BPF and PPF were the same:



yearID park TeamAL TeamNL BPFal PPFnl
1921 Polo Grounds IV New York Yankees New York Giants 102 98
1922 Polo Grounds IV New York Yankees New York Giants 102 98


Park factor is used to compute OPS+ and ERA+, two bedrocks of current conventional wisdom.  I realize that parks change from one season to the next, even the configuration of the same park changes, and that there are different parks in the two leagues but this indicates how little we know about this important stat other than the vague notion that it somehow mysteriously takes the different and non-uniform playing areas into account in order to enable us to compare Albert Pujols and Lou Gehrig.

We really should have a much better understanding of park factor.  Wins Above Replacement (WAR).  All that stuff.

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