— Where BTF's Members Investigate the Grand Old Game
Monday, March 10, 2003
Baserunning Park Factors
Do ballparks have a measurable impact on taking that extra base?
We all know that ballparks have a significant impact on offense. They have an impact on home runs, strikeouts and other hitting and pitching elements. In the past couple of years, we?ve even come to understand that ballparks have an impact on defense. But did you know that ballparks also have an impact on baserunning?
At least, this is the conclusion I came to after analyzing some baseball statistics, courtesy of Ray Kerby?s Astros Statistical Software (aka ASS).
Here?s what I did. I pulled data for four years (1999 to 2002) and calculated each team?s baserunning performance at home and on the road. Specifically, I reviewed how often each team:
I then calculated how often the baserunner on first made it to third or home, and I looked at the difference between home games and away games. Here are the results:
Keep in mind that the "Diff" column is expressed in percentage points. Expressed in pure percentage terms, Atlanta baserunners were 33% more likely to advance that extra base at home vs. on the road.
You may have noticed that Colorado was very good at getting runners to third or home both at home and on the road. I have no idea why.
Four years data represents about 800 total at bats; half at home and half on the road. This should be large enough to achieve statistical significance and "blend" any specific situational biases, such as number of outs or baserunner speed.
To be sure, I calculated the same statistic for each year in the four year period. Here are the results:
This data verifies that the results are real, at least for the extreme cases of Atlanta, Texas and San Diego. I?ll let you draw your own conclusions about the other parks.
Don?t forget that Detroit, Pittsburgh, San Francisco, Houston and Milwaukee all moved to new parks during this time period. It?s interesting to note the impact Miller Park and PNC Park had on their respective team?s baserunning results, in particular.
So how big is this impact? Well, this situation occurred about 100 at bats for each team in a season. Pete Palmer?s old run chart from the Hidden Game of Baseball indicates that difference between second and third is about .2 runs. This means that Atlanta added six or seven runs (.2*33%*100) as a result of Turner Field?s baserunning factor. Given that they scored about 360 runs at home last year, this means that baserunning increased scoring at home about two percent.
However, this is certainly understated. First of all, Palmer?s run expectancy probably underestimates the impact of advanced bases in these run-inflated times. But more importantly, it seems likely that these parks have a similar impact on other baserunning situations. A 3% to 4% impact seems likely for the extreme ballparks.
This is what the data says. Anyone know why?