Home Cookin'

For as long as baseball has been played home teams have played better than road teams. Part of this is batting last in the inning but also people have guessed that sleeping in your own bed, playing in front of a cheering crowd, and familiarity with your home ballpark has played a roll. Up until recently it has been difficult to separate these effects from one another. Just how much of home field advantage is the knowledge of your home park for instance?

For instance, maybe your home park has a slightly tilted center field.

Maybe you have to deal with a giant wall that balls keep bouncing off of.

Maybe when you look up to catch a flyball you see this.


In 2001 MLB moved to an unbalanced schedule. Before, every team in your league came to your park the same number of times (though because of some two and four game series not exactly the same number of games). In 2001 and beyond teams starting playing many more games against other teams in their division. Now, most teams from the other divisions in your league would only travel to your park once a year, and teams in your division would play in your park for three series. This has created a group of teams that should be very familiar with your home park and a group of teams that should be unfamiliar. This study will check if there is any difference between how well home teams play against those two groups.

For each year from 1996 I broke up each team's home schedule up into three groups. The first group was games against teams in the same division. The second group was games against teams in other divisions, but in the same league. The third group was interleague games. I then estimated how many games each team should win for each group by adjusting for the strength of schedule for each game. Here are the results for 2006 by team.



div, lg, and i are the three groups: division games, league games but not divisional, and interleague games. E(d), E(l), and E(i) are the estimated wins for those groups. Note because a team usually has about a 53% chance of winning each home game these estimates are not integers.

If we look at the Cubs as an example, they play in a six team division so they are playing a huge number of divisional games. Even though they had the second worst record in baseball, they still were estimated to win about 20 home games in the division (thanks to a terrible NL central as well). When we look at league games and interleague games then they don't fair as well.

So now we are going to add those up for each team to get yearly numbers.


You can see that before 2001 teams were playing many more home games against other teams not in their division. After 2001 the home games were split rather evenly. Interleague play started in 1997. You would have expected that teams would have done better at the start of interleague play but that doesn't seem to be the case. So now to determine just how much the home field advantage changes.

I am using years 1996-2000 as the control sample where teams should play just as well out of division as they do in the division for league games. From years 2002-2007 teams should play better out of their division than inside it if the opponents are having trouble adjusting to the home park. You will notice that I am not including 2001 in either sample. 2001 was the first year of the unbalanced schedule so the previous year teams still saw the home team's park two timws so I don't feel right about adding it to the unbalanced years. On the other hand, teams were only making one trip to a non-divisional park so I don't feel right about adding it to the balanced years. So I am leaving that year out altogether. Fortunately, it doesn't really change the results either way.



Again, the first column is the divisional games, the second is League games, and the last is interleague. It appears that home field advantage has increased in recent years but the difference between the league games and the divisional games has stayed the same. This means that road teams aren't really affected by the playing in an unfamiliar park. This goes to show just how well teams prepare for games. The interleague games show the highest difference but the change in DH rules probably is most of the effect.