An index of how much a ballpark inflates or suppresses a given outcome compared with a neutral park, where 100 is average.
Park factors normalize for the fact that stadiums are not equal: altitude, dimensions, wall heights, and foul territory all shift how often runs, home runs, and extra-base hits occur. A home-run park factor above 100 means the park boosts home runs relative to league average; below 100 means it suppresses them.
BallBet uses multi-year stadium baselines that are stable from game to game, then layers same-day weather — temperature, wind speed and direction — on top, since conditions can move a neutral park meaningfully on a given night.
Park factor is a multiplier on every home-run and total-bases read. A power hitter in a home-run-friendly park with the wind blowing out is a different proposition than the same hitter in a pitcher's park.
100 is neutral — the park plays at the league average for that outcome. Above 100 means the park inflates it (a hitter's park for that stat); below 100 means it suppresses it (a pitcher's park).
The stadium baseline is a multi-year figure that is stable. What changes nightly is weather — temperature and wind — which BallBet layers on top of the baseline for each game.