Batting park factor
Batting Park Factor, also simply called Park Factor or BPF, is a baseball statistic that indicates the difference between runs scored in a team's home and road games. Most commonly used as a metric in the sabermetric community, it has found more general usage in recent years. It is helpful in assessing how much a specific ballpark contributes to the offensive production of a team or player.
The formula most commonly used is:
In this formula, all runs scored by or against a team at home are divided by all runs scored on the road. Parks with a Park Factor over 100 are those where more overall runs are scored when the team is at home than are scored when the team is away. While some variation can be attributable to fluctuations in offensive and defensive performance, PF accounts for the production of both teams in each park and, correspondingly, is very useful in determining which actual ballparks are "hitter friendly" and which are "pitcher friendly". One criticism is that Park Factor does not account for differences in pitching between teams. An above average pitching staff may distort their home stadium's Park Factor by making it seem more pitcher-friendly than it really is.