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August 16, 2004

How Parks Affect Baserunning

Looking for the Home-Field Advantage

by James Click

One of baseball’s hoary adages is the idea that if a team can manage to play .500 ball on the road, they’re likely to make the playoffs. The saying relies on the fact that that home teams should do much better than break-even, because they enjoy inherent advantages over the visiting team. In fact, home teams win more than their fair share of games, somewhere around 54% with slight variances from year to year. Checking the standings this year shows that just nine teams have a winning road record, most by just a game or three.

The source of this advantage is unknown. It's been suggested that local knowledge, how to hit or pitch better in a team’s more familiar home park, is the key. Perhaps some of the home team’s advantage lies in knowing the nuances of their particular ballpark, but applied in a different area. It’s possible that home teams may be better baserunners, knowing better than their opponents which balls will allow them to take the extra base.

Before getting into whether or not a baserunning advantage is the result of a particular park, it’s important to first establish that parks do affect the baserunning in a consistent manner from year to year. To determine if park factors for baserunning do exist, I’ll look at three typical baserunning situations where the runner is faced with the choice to take the extra base or not: a runner on first during a single, a runner on first during a double, and a runner on second during a single. There are three possible outcomes to each baserunning event: the runner can take the base he's supposed to, the runner can take the extra base or the runner can be thrown out.

When creating the park factors, I’ll follow the lead of Keith Woolner’s analysis of catchers and the stolen base in Baseball Prospectus 2004; the consistency from year to year will be measured both by the number of attempts for the extra base (aggressiveness on the basepaths) and the success rate when attempting to take it. Additionally, since the sample size of baserunning can be small, I’ll look at five-year blocks of baserunning data.

Comparing each five-year block by stadium to the next five years, and broken down by baserunning situation and home and visiting teams, yields the following correlations:

Attempt Rate

             First to Third    First to Home    Second to Home       Total
Home             .6388             .6257             .6441           .6492
Visitor          .6337             .6399             .6388           .6479
Total                                                                .6508

Success Rate

             First to Third    First to Home    Second to Home       Total
Home             .6338             .6291             .6387           .6367
Visitor          .6370             .6217             .6380           .6399
Total                                                                .6383

The correlation from five-year block to five-year block is startlingly consistent. The correlation rate is high enough that we can confidently say that parks do have a consistent effect on baserunning, both in attempt rate and success rate. Furthermore, the correlation from five-year block to five-year block is very consistent, even when broken down by baserunning situation and home or visiting team. This result supports the idea that various parks affect the individual situations consistently from year to year, and therefore, park factors can be applied to the individual situation as well as to the overall baserunning data.