Do Unique Ballparks provide a larger than normal home field advantage?

Last updated August 15, 1997

Goto Hitter's Parks, Pithcher's Parks, Summary

In Rob Neyer's July 21, 1997 Chin Muzak he observes that both the Rockies and Burt Shotton's Phillies had extreme Home/Road splits while playing in extreme hitters parks and asks "Can it be coincidental that they happen to play in perhaps the best hitter's parks ever?" Rob also had followup columns discussing letters from Guy Tyler on August 8 and from Chris Aberson and John Rickert(me) on August 15. A further followup from Tim Ruane was printed August 19. Here's a start at looking at the question.

Hitter's Parks

I went through the latest edition of Total Baseball and listed teams with batters park factors of 105 or greater. (i.e. the park inflates offense by 4.5% or more) I then found all teams that maintained such a large park factor for five or more seasons. Since several teams dipped slightly below 105 for a season and came back, I expended the list to also include teams with 6 or more seasons with only one year of batters park factor below 105.

I then used the Baseball Encyclopedia to find the records at home and on the road for each team and compiled the results. A summary is in the table below:
Team Years W-L Pct. Home Road Difference
Red Sox 1989-94 462-463 .499 258-211 .550 204-252 .447 .103
Braves 1983-92 749-865 .464 396-409 .492 353-456 .436 .056
Cubs 1983-91 714-737 .492 389-338 .535 325-399 .449 .086
Red Sox 1964-84 1761-1574 .528 953-715 .571 808-859 .485 .086
Cubs 1976-80 379-431 .468 214-192 .527 165-239 .408 .119
Cubs 1967-73 592-533 .526 322-241 .572 270-292 .480 .092
Reds 1963-69 602-530 .532 327-238 .579 275-292 .485 .094
Cardinals 1959-65 587-522 .529 328-227 .591 259-295 .468 .123
Dodgers 1956-61 507-419 .548 267-196 .577 240-223 .518 .059
Red Sox 1946-59 1193-963 .553 683-396 .633 510-567 .474 .159
Tigers 1938-46 749-636 .541 412-285 .591 337-351 .490 .101
Cardinals 1938-42 450-314 .589 241-145 .624 209-169 .553 .071
Phillies 1929-37 562-814 .408 320-359 .471 242-455 .347 .124
Phillies 1918-26 503-826 .378 266-391 .405 237-435 .353 .052
Browns 1921-26 466-453 .507 263-200 .568 203-253 .445 .123
Highlanders 1903-07 395-338 .539 213-153 .582 182-185 .496 .086
TOTAL 10,671-10,418 .506 5852-4696 .555 4819-5722 .457 .098
The won-lost percentage for home teams for 1900-1995 was .542, so road teams W-L Pct. was .458 and the difference was .084.

The overall road Pct. for the teams was .457, very close to a normal road percentage. If we decide that this means that the teams were overall average teams, then their home winning percentage should be .541. Instead, it was .555. If we assume that the teams were average teams, then the probability of deviating that far from the expected number of wins at home is approximately 0.9%, indicating that there probably is a small advantage for teams playing in extreme hitters parks.
Of course, an alternative explanation is that the teams were really slightly better than average, as was indicated by their overall .506 W-L pct. If this assumption is used then the teams would come out better at home (but only at the 17% confidence level) and worse on the road (also at a 17% level), however the results are not statistically significant.

The likelihood of average teams deviating as far from .500 as .506(or farther) is roughly 25%. again, not an unreasonable occurance.


There were also eight teams that played in offensive parks for four consecutive years, or four out of five years. They produced the following results:
Team Years W-L Pct. Home Road Difference
Rockies 1993-96 280-305 .479 163-128 .560 117-177 .398 .162
Braves 1976-79 266-380 .412 147-175 .457 119-205 .367 .090
Braves 1970-73 304-335 .476 161-159 .503 143-176 .448 .055
Reds 1955-58 322-294 .523 182-126 .591 140-168 .455 .136
Browns 1932-35 250-359 .411 130-171 .432 120-188 .390 .042
Red Sox 1934-38 396-364 .521 226-153 .596 170-211 .446 .150
Indians 1916-19 322-252 .561 169-114 .597 153-138 .526 .071
Reds 1902-05 311-274 .532 175-125 .583 136-149 .477 .106
TOTAL 2451-2563 .489 1353-1151 .540 1098-1412 .437 .103

The `Best' Hitter's Parks

Here's a list of the highest Batter Park Factors from Total Baseball:
  • 129 Colorado NL 1995-6
  • 116 Colorado NL 1993-4
  • 115 Chicago NL 1971
  • 113 Chicago NL 1969, Philadelphia NL 1933-4
  • 112 Boston AL 1976-7, Chicago NL 1978, Atlanta NL 1977, Chicago NL 1970, Boston AL 1956, Philadelphia NL 1932 Philadelphia NL 1923-4, Boston NL 1900
  • 111 Chicago NL 1985, Atlanta NL 1978, Chicago NL 1977, Boston AL 1978, Cincinnati NL 1967, Los Angeles AL 1961 Boston AL 1954, Chicago NL 1916, New York AL 1905 Cincinnati NL 1903,05
  • 110 Boston AL 1966, St. Louis NL 1961-2, Brooklyn NL 1957 Boston AL 1950-1, Detroit AL 1940-1*, Philadelphia NL 1935-6 Cleveland AL 1918, Cincinnati NL 1902

    The won-lost records for these teams (data from Pete Palmer) were

    BPF W-L Pct. Home Road Difference
    129 160-146 .523 99-54 .647 61-92 .399 .248
    116 120-159 .430 64-74 .464 56-85 .397 .067
    115 83-79 .512 44-37 .543 39-42 .481 .062
    113 208-255 .449 116-108 .518 92-147 .385 .133
    112 737-823 .472 403-376 .517 334-447 .428 .090
    111 843-876 .490 486-385 .558 357-491 .421 .137
    110 927-895 .509 511-399 .562 416-496 .456 .105
    TOTAL 3078-3233 .488 1723-1433 .546 1355-1800 .429 .116
    Difference is calculated using more than 3 decimal places, so rounding error might occasionally make the Difference value appear incorrect.

    The Rockies are clearly an outlier on this chart, but the trend is not entirely clear. The teams in the next best hitters parks, The Rockies in Mile High and the Cubs in Wrigley, had below average differences.
    When we get to the BPFs with several teams, the numbers seem to be staying around a slightly larger than normal difference.
    *I received a note from DaveB saying:
    Recently I watched "The Life and Times of Hank Greenberg" and in the film, he talked about how in 1940 the main reason for the Tigers success (they won the Pennant) was the fact that they were stealing signs. They only did this at home as they had a guy in the upper deck bleachers of Briggs Stadium with binoculars giving them signals. Greenberg said that he and Rudy York were getting fat HR numbers during this time. I'm not sure for how many years this went on, but it is very interesting that one of the largest park factors in the history of baseball occurred at Briggs stadium from 1940-1941. I'm quite certain that the sign-stealing was the main contributor to the high home Batter Park Factor of that Tiger era.

    Pitcher's Parks

    There were twelve teams that played in "pitcher's parks". (batters park factor of no more than 95 for either 5 or more consecutive years or for all but one of 6 consecutive years) Their overall won-lost percentage was .482. At home they were .531, on the road .434, a difference of .097.
    Team Years W-L Pct. Home Road Difference
    A's 1991-95 366-378 .492 198-173 .534 168-205 .450 .084
    A's 1978-87 723-844 .461 402-380 .514 321-464 .409 .105
    Astros 1975-84 784-784 .500 449-333 .574 335-451 .426 .148
    Padres 1971-82 799-1082 .425 438-506 .464 361-576 .385 .079
    Angels 1971-76 446-518 .463 231-257 .476 215-264 .449 .027
    Dodgers 1962-71 883-739 .544 465-347 .573 418-392 .516 .057
    Astros 1962-66 333-475 .412 198-206 .491 135-269 .334 .157
    Braves 1949-61 1100-903 .549 581-418 .582 519-485 .517 .065
    Orioles 1954-58 330-437 .430 191-192 .499 139-245 .357 .142
    Braves 1933-40 554-665 .454 305-297 .507 249-368 .404 .103
    Yankees 1931-35 475-285 .625 258-120 .683 217-165 .568 .115
    Senators 1906-10 279-477 .369 168-203 .453 111-274 .288 .165
    TOTAL 7072-7587 .482 3884-3429 .531 3188-4158 .434 .097

    Summary

    Category W-L Pct. Difference
    Extreme Hitter 3078-3233 .488 .116
    Long-Term Hitter 10,6711-10,418 .506 .098
    Med.-Term Hitter 2451-2563 .489 .103
    All .500 .084
    Long-Term Pitcher 7072-7587 .482 .097
    This is (thin) evidence that there is an effect and that it grows stronger in more extreme parks, but it'll take some statistical tools to pull it out. What I suspect is that the Rockies extreme split is mostly a coincidence and that (much like the Twins a dozen years ago) their Home/Road splits will move closer to normal.

    After all, what is "uniqueness"? Are the Metrodome, Kaufmann Stadium, Forbes Field and the Polo Grounds unique if their effect on runs scored is close to zero? If so, which is `uniquer', a "neutral" Polo Grounds, a hitter's Coors Field or a pitcher's Astrodome?

    Further study is needed to answer the question, but there might be an effect. If it exists it's small - worth maybe one win a year. Not much, though the 1978 Red Sox and the 1967 Red Sox, might disagree


    Further things to look at

  • Teams playing in pitchers parks for four consecutive seasons (there are three)
  • Teams with `park factors' of 100
  • Teams in short-term `extreme' pitcher's parks
  • There's probably something else...

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