Baseball is rare among professional sports in that the playing field is not standardized. The official rules of baseball provide for precise measurements within the infield, but only a few guidelines for distances to the outfield fences, leaving room for a wide variety of shapes, sizes, playing surfaces, building types, and so on. Combine these physical variations with the effects of altitude and climate in different parts of the country, and you can easily see how a ballpark can exert a large influence on games played there.
For this reason, ballparks play a large role in DMB. When players are created, their raw statistics are adjusted for the statistical impact of their home park. This (along with the era-based adjustments) helps us create park-neutral ratings for all players. And when you play a DMB game, the nature of the home park plays a significant role in the outcomes of games played there.
These park adjustments add realism to your DMB games. If you use the real-life rosters and the real-life schedule, the park effects that are removed during player creation are cancelled out by those that are added during game play, so the players will produce statistics in DMB that are very consistent with their real-life stats. If, on the other hand, you draft new rosters, many of your players will be playing their DMB games in different parks than in real life, and the change in parks will have an impact on their DMB statistics.
This is the way it should be. In real-life, when a hitter is traded to a hitter-friendly park, you expect their statistics to rise even if their talent level doesn't change, and you discount their real-life stats for the effects of their new home park. The same is true in DMB. If you move a player to a new park that is quite different from his real-life park, you can expect to see his statistics be affected by this move.
In DMB, the influence of a ballpark is reflected in the following four groups of park attributes and ratings:
General park information, such as its name and location
Physical characteristics, such as the distance and height of the fences
Weather patterns, including temperature, wind direction and wind speed
Statistical park factors that sum up the overall impact of the park on the rates of singles, doubles, triples and homeruns that are produced in that park by left- and right-handed batters
... we haven't yet figured out how to isolate all of the things that affects the statistics produced in a ballpark. How much will the rates of doubles, triples and homers be affected by a 20-foot change in wall distance? By raising the fence by 10 feet? By putting in a new type of artificial turf? Adding a new tier of seats that changes the wind patterns? Or blocking off the center field seats so hitters can see the pitched ball better? We don't know for sure.
But we can measure the overall impact of each park through careful study of home and road statistics, and we can capture that overall impact through the statistical park factors. If a park consistently increases doubles by 30%, we can give the park a rating that will produce a 30% increase in your DMB games. To that extent, we don't need to know precisely how much each of the factors is contributing to this 30% figure.
Statistical Park Factors
You can change the park's impact on the number of singles, doubles, triples, and homeruns hit by left- and right-handed batters. These numbers can range from 20 to 500, with an average park having a rating of 100. If the park allows only 58% as many homeruns as the average ballpark, the homerun rating for that park is 58. And if a park allowed 40% more triples than average, its triples rating is 140.
Here's an example. If a team's road games included 140 homeruns and its home games included 100 (both for and against), you can conclude that the home park allows only 100 / 140 = 71% as many homers as the average of the other parks in the league. So you would assign a homerun factor of 71 for this park.
It is unusual for a singles rating to be outside the range from 85-115, because there are very few ways that a park can affect the number of singles that are hit. The ranges for modern stadiums are usually 70-130 for doubles, 50-200 for triples, and 50-150 for homeruns. Many years ago, there was more variety in stadiums, and larger differences in park ratings were more common.