Everything You've Wanted to Know About Park Factors

It’s no secret that analytics has had a greater impact on baseball than most, if not all other major sports. A leading reason for this is that the fundamental building block of any baseball event, a pitch, is a relatively isolated event. Sure, there are eight other players on the field, but it’s primarily a 1 vs. 1 interaction between a batter and a pitcher. Analysts covering other sports aren’t so lucky; basketball, football, soccer, and hockey all have an entire defensive staff that’s able to adjust its coverage of a player, and several teammates whose activity can have a positive or negative influence on a player’s output in hard-to-measure ways. The relative lack of outside factors influencing a pitching event, paired with the large sample size created by a long season, means that we can typically understand a player or team’s skill with a high degree of confidence.

Events in two different baseball games aren’t perfectly comparable, though. One significant factor that complicates our ability to compare one player’s performance to another’s is the ballpark factor. Unlike other sports, whose arenas have highly-regulated rules surrounding their dimensions, each baseball stadium is unique in its size and shape. Fenway Park’s center field fence is just 390ft. from home plate, while Minute Maid’s is much farther out at 436. Simply put, a home run in Boston may not have been a home run in Houston. The below image from Thirty81 Project's Lou Spirito is a nice depiction of the extreme variations between different ballparks’ dimensions (h/t Matt Monagan whose writing for Cut4 pointed me here). The full visual has a lot more detail, you can check it out here.

Climate conditions complicate this further. Some stadiums are open-air, while others can be covered. The Rockies play at an extreme altitude where the ball naturally flies farther, while the Yankees play close to sea level.

All this means that, while baseball does have the luxury of clean, 1 vs. 1 interactions whose results can be easily analyzed, we need a way to adjust for differences in venues to accurately compare one player or team’s performance to another’s.

Fortunately, the impact that a stadium has on player performance is measurable and can be applied to adjust a player’s performance to account for the stadiums they’ve played in, creating stadium-agnostic statistics. This post will