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August 16, 2004
How Parks Affect Baserunning
Looking for the Home-Field Advantage
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.
However, for the time being, looking at each individual situation isn't likely to shed light on the issue of home-field advantage and baserunning. Therefore, for each park, rather than looking at each individual baserunning situation, I'll tally the results of all three and see if there is an inherent advantage to running in a team's home park. (If you're interested in how the third-base coaches affect baserunning, check out Michael Wolverton's excellent piece.)
Here are the attempt rates for each park over the past five seasons (newly opened parks include data for as long as they've been open):
Attempt Rates Park Total Home Visitor Diff Coors Field .484 .542 .424 .118 Miller Park .455 .409 .460 -.051 Wrigley Field .448 .412 .489 -.077 Comerica Park .446 .447 .444 .003 Kauffman Stadium .444 .440 .448 -.008 Ameriquest Field .443 .462 .425 .037 PNC Park .442 .418 .428 -.010 Turner Field .442 .456 .428 .028 Great American BP .440 .414 .432 -.018 Petco Park .432 .443 .432 .011 Busch Stadium .428 .442 .410 .032 Dodger Stadium .428 .414 .443 -.029 Bank One Ballpark .427 .441 .411 .030 Citizens Bank Park .426 .475 .431 .044 Yankee Stadium .425 .429 .421 .008 Angel Stadium .422 .446 .398 .048 Jacobs Field .418 .420 .417 .003 US Cellular Field .418 .421 .416 .005 Minute Maid Park .418 .418 .418 .000 Metrodome .417 .449 .387 .062 Camden Yards .416 .417 .415 .002 ProPlayer Stadium .412 .406 .418 -.012 Shea Stadium .412 .430 .394 .036 Tropicana Field .410 .417 .403 .014 Network Associates .408 .413 .402 .011 SBC Park .405 .395 .415 -.020 Fenway Park .401 .381 .425 -.044 SafeCo Field .400 .408 .391 .017 Olympic Stadium .384 .406 .363 .043 SkyDome .373 .365 .380 -.015
Looking at these numbers, we can draw several conclusions. Coors Field yields, by far, the most attempts at the extra base. This is due mostly to the fact that the Rockies are such an aggressive baserunning team in their home park. In fact, the Rockies have attempted to nab the extra base 54.2% of the time over the past five seasons at home, while their opponents have run at about a league average rate of 42.4%. While some of this may be due to the Rockies' botched "speed-and-defense" plan to counteract the affects of altitude, the fact that the Rocks have attempted the extra base at the league-average rate while on the road over the past five years indicates that the effect is largely due to the environment.
To some degree, the larger ballparks appear at the top of the list while the smaller parks tend to be towards the bottom. Colorado, Detroit, Kansas City and Texas are all near the top, while Houston, Baltimore and even Boston and San Francisco (short porches with deep center fields) are all nearer the bottom. This result is by no means determinative, but there does appear to be a slight trend.
The artificial turf parks (Minnesota, Montreal, Tampa Bay and Toronto) are all in the bottom half of the list, but they do show a slight trend towards home-field advantage. After the Rockies, the Twins enjoy the highest positive differential in baserunning aggressiveness over the past five years, perhaps due to their unique playing environment. Montreal also shows a significant home-field advantage, Tampa's is slightly positive, and Toronto, bringing up the rear, is slightly negative.
It should also be noted that while year-to-year changes in park factors are usually due to normal statistical variance, weather, and other influences, occasionally the park itself physically changes. For instance, Comerica Field's fences were moved in prior to the 2003 season, and Kauffman Stadium's walls were moved out last winter. While it's overkill to scrap the data from before the change and treat the new dimensions as a new park, checking how the new fence distances changed the data can be informative.
In this case, however, it's simply confusing. In Kansas City, the attempt rate has gone up very slightly so far this year with the larger dimensions, while in Detroit the attempt rate has actually risen dramatically (from about .435 to .464) since the fences were moved in. With a few more years of data, firmer conclusions can be drawn, but for the time being, this data point shoots a nice hole in the idea that larger parks yield more aggressive baserunners.
Coors Field aside, there is no consistent, league-wide advantage for the home team when it comes to attempting the extra base. Since the difference between the home team's and away team's aggressiveness on the basepaths is somewhat evenly distributed from top to bottom, it's unlikely that the negative numbers simply indicate bad baserunning teams.
Looking now at the success rates in the various parks:
Success Rates Park Total Home Visitor Diff Ameriquest Field .965 .957 .974 -.017 SkyDome .963 .952 .972 -.020 Network Associates .960 .952 .969 -.017 Coors Field .959 .966 .951 .015 Bank One Ballpark .957 .959 .956 .003 Comerica Park .955 .957 .952 .005 Yankee Stadium .955 .938 .972 -.034 Kauffman Stadium .954 .953 .955 -.002 SafeCo Field .953 .941 .968 -.027 SBC Park .952 .942 .962 -.020 Wrigley Field .952 .938 .965 -.027 Miller Park .949 .922 .947 -.025 Busch Stadium .949 .949 .950 -.001 US Cellular Field .948 .948 .948 .000 Camden Yards .948 .939 .956 -.017 Metrodome .946 .946 .945 .001 Dodger Stadium .945 .949 .940 .009 Angel Stadium .945 .952 .936 .016 Shea Stadium .945 .936 .954 -.018 PNC Park .941 .936 .934 .002 Minute Maid Park .941 .948 .932 .016 Tropicana Field .941 .937 .945 -.008 ProPlayer Stadium .940 .932 .947 -.015 Jacobs Field .939 .932 .945 -.013 Olympic Stadium .939 .966 .909 .057 Fenway Park .938 .928 .949 -.021 Turner Field .936 .935 .937 -.002 Great American BP .934 .920 .925 -.005 Citizens Bank Park .931 .907 .924 -.017 Petco Park .929 .966 .923 .043
The primary difference between this data and the chart above is that the variance in success rates is much tighter than the variance of attempt rates. On the whole, most teams are equally successful when attempting to take the extra base. Furthermore, the difference between the success of the home team and the away team is much smaller than the difference in attempts. However, we can still draw a few conclusions.
Baseball's three newest parks are the three lowest parks on the list: Cincinnati, Philadelphia and San Diego. The fact that all three are at the bottom of the list may simply be due to small sample size issues, but it may also be a byproduct of players not having played in the parks very much. It will be interesting to see if they move to the middle of the pack as players get used to the bounce of the ball in these new outfields.
Toronto makes a dramatic turnaround and rockets from the bottom of the list to the #2 slot. While the Blue Jays themselves could be said to be selectively effective when running the bases--only taking the extra base when they are virtually assured of success--their failure to cut down their opponents, who appear equally as conservative, is also a large factor. Likewise, Texas, Oakland and Seattle are three of the four worst teams at throwing out opposing runners stretching for the extra base in their home park.
In general, the National League appears to be a poorer baserunning group than the junior circuit, a difference that may be due to the presence of the occasional pitcher on the basepath. Given how infrequently pitchers do actually get on base, however, it's difficult to place that overall discrepancy on their narrow shoulders.
Getting back to the original question about home-field advantage in baserunning, the data shows that, while there may be a few parks in which the home team does show a consistent, sizeable advantage, in general, the road team has been equally as aggressive and successful. For the time being, we'll have to concede that perhaps home-field advantage does actually have something to do with hotel beds, room service and only having 12 channels on television.