Moving the Fences: A Follow-Up

On Monday, I looked at a few ballparks that, in the past, had moved in their fences in an attempt to make the park more hitter-friendly. The Royals did it in the mid-90s, the Tigers did it between 2002-2003, the Padres did it between 2005-2006, and the Mets did it between 2011-2012. This very offseason, the Padres are doing it again, and the Mariners are doing it as well. Based on data, the home-run factors for each ballpark went up after the adjustments, but the run-scoring factors didn’t, which I found to be of interest.

This post, as indicated, is a follow-up, made necessary for two reasons. For one, I overlooked the White Sox, who, between 2000-2001, moved in the fences in what’s now known as U.S. Cellular Field. I don’t know how that escaped my attention before. For two, if we’re going to look at places that moved in the fences, we should also look at places that moved out the fences, because we can learn from those examples too. Between 2003-2004, the Royals moved the fences in Kauffman back to where they were long before, prior to the adjustments in the 90s. And, between 2005-2006, the Phillies made adjustments at Citizens Bank Park, in response to the feeling the place was a bandbox. Once again, we examine the data, in order.

U.S. Cellular Field

U.S. Cellular has undergone a lot of renovations, and down the two foul lines, the fences were moved in before 2001, making room for the bullpens and the Bullpen Sports Bar. At least, that’s what Wikipedia is telling me. It’s not that anybody thought U.S. Cellular was too pitcher-friendly, I don’t think. Over three years, between 1998-2000, the home-run rate at U.S. Cellular was 107% the home-run rate in White Sox games on the road. Over the same three years, the run-scoring rate at U.S. Cellular was 101% the run-scoring rate in White Sox games on the road. Over the next three years, between 2001-2003, the home-run rate at U.S. Cellular was 126% the home-run rate in White Sox games on the road. The run-scoring rate at U.S. Cellular was 103% the run-scoring rate in White Sox games on the road. Homers went way up; runs went up a very tiny bit. We know U.S. Cellular today as something of a bandbox.

Kauffman Stadium

And so we re-visit the home of the Royals, who between 2003-2004 changed their minds from the decade before. Now we’re talking about fences being moved back, and not in. Over three years, between 2001-2003, the home-run rate at Kauffman was 114% the home-run rate in Royals games on the road. Over the same three years, the run-scoring rate at Kauffman was 128% the run-scoring rate in Royals games on the road. Over the next three years, between 2004-2006, the home-run rate at Kauffman was 80% the home-run rate in Royals games on the road. The run-scoring rate at Kauffman was 101% the run-scoring rate in Royals games on the road. Homers went way down, and runs also went way down.

But this is odd. As we noted yesterday, after the Royals first moved the fences in, the park played neutrally, if somewhat pitcher-friendly. Over the course of some years, the park started to play hitter-friendly. There were no dimension adjustments, so I’m left thinking about the sample sizes we’re dealing with. Kauffman probably wasn’t as neutral as it seemed immediately following the first change, and it probably wasn’t as extreme as it seemed prior to the second change.

Citizens Bank Park

It took just two years for the Phillies to decide their new stadium was too kind to hitters, and too rude to pitchers. So back went some of the fences, as the Phillies tried to even things out. Over two years, between 2004-2005, the home-run rate at Citizens Bank was 119% the home-run rate in Phillies games on the road. Over the same two years, the run-scoring rate at Citizens Bank was 109% the run-scoring rate in Phillies games on the road. Over the next three years, between 2006-2008, the home-run rate at Citizens Bank was actually 123% the home-run rate in Phillies games on the road. The run-scoring rate at Citizens Bank was 104% the run-scoring rate in Phillies games on the road. While, over the years observed, homers didn’t go down, runs went down, which was basically the idea. Citizens Bank developed a certain reputation early on, but these days it’s unobjectionable.

Now we have a better understanding of all the data, and we also have this helpful comment from Monday from MGL. When fences have gotten moved in, homers have become easier to hit, but there hasn’t been much impact on overall run scoring, probably owing to reduced singles, doubles, and/or triples. When fences have gotten moved out, there seems to have been an impact on overall run scoring, as runs have gone down, relative to runs on the road. Citizens Bank is a little tricky to figure out, based on our window above, but the FanGraphs park factors suggest the homer factor is now lower than it was. So that’s more intuitive.

My number-one conclusion is that I wish we had more examples of ballparks changing their dimensions. My number-two conclusion is that park factors are complicated, and effects of changes aren’t always easy to predict. You might be able to predict effects on specific things — changing the fences does seem to change home-run rates — but, overall, there are a lot of moving parts, a lot of things to put together. As far as the Mariners and Padres are concerned, 2013 should bring more frequent home runs than 2012 and seasons before. But in terms of the ease of run scoring, Safeco and Petco might change surprisingly little. There’s reason to believe it’ll be easier to score down the road, but the magnitude of the increased ease could be quite modest.