One of the very most important principles in the field of baseball analysis is the concept of park factors — having an understanding that the game can play differently depending on the environment. I don’t think this is unique to baseball, but it’s most evident in baseball, where a game in old Coors Field would be very different from a game in recent Petco Park. All decent analysis has to take park factors into account. Otherwise, you’re just leaving way too much off the table.
But most people, when they think of park factors, consider what happens to the baseball once it’s put in play. This park increases doubles; this other park reduces home runs. These are the easiest park factors to understand, absolutely, and they’re generally the easiest to explain. Fenway Park has the Green Monster, which does things. Coors Field is at elevation, which does other things. I don’t need to explain this stuff to you.
But far fewer people think about parks having an effect on walks and strikeouts. These effects are less intuitive, but they exist, and they’re worth highlighting because they don’t get enough attention. You’ll find some walk and strikeout factors here, on the FanGraphs Guts page, but you won’t find them here, on the FanGraphs handedness Guts page. So below I’m just going to insert a simple table of data. You’ll find all teams, corresponding to those teams’ home stadiums. Data is for 2010-2012, for all stadiums except Marlins Park, for which we have only 2012 data. You’ll see two data columns: uBB% and SO%. The former refers to unintentional walk rate at home, divided by unintentional walk rate away. The latter refers to strikeout rate at home, divided by strikeout rate away. All home and road numbers are combined, and while this is pretty simple and could be adjusted for the sake of improving accuracy, this’ll get us most of the way there.
In theory, the table is sortable!
The most extreme effect observed is that U.S. Cellular has increased walk rate by 20%. It’s also increased strikeout rate, but by only 4%. One explanation might be that U.S. Cellular is small, and pitchers are more likely to nibble out of fear of allowing a dinger, but then Safeco Field has had the next-highest walk-rate boost so who knows? There are probably several explanations that go into each number seen.
Nationals Park, meanwhile, has greatly reduced walks, while PNC has significantly reduced both walks and strikeouts. Safeco and Petco Park have allowed for the greatest strikeout-rate boosts, and it’ll be interesting to see if these numbers change going forward, now that both stadiums are getting dimension adjustments to become less pitcher-friendly. It’s not a surprise to see that Coors Field drives strikeouts down, but it might be a surprise to see Comerica Park reducing strikeouts, too. The Marlins used to play in a strikeout-heavy stadium, but early results suggest that Marlins Park won’t play in the same way.
Nothing in here is novel, and many of you have seen stuff like this before. I was first made aware of walk and strikeout park factors years ago, myself. But these things are easy to ignore, when in truth they can be pretty meaningful. Anything can affect everything, and there can be a lot more to a ballpark than you might figure.