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Supreme Splits Part 1: Home and Road

Posted by Andy
Long before the introduction of all the advanced metrics available on Baseball-Reference.com, Sean posted all sorts of splits, and I fell in love with them immediately. I think there is no better basic analysis that reveals so much beyond basic stat lines.

I'm working up a few posts showing just how cool splits can be, even with just a cursory examination.

Starting off, here's a look at home/road splits.

It probably comes as no surprise that teams hit better at home than they do on the road. The home/road splits across all of MLB in 2011 can be found right here.

The basics are as follows:

Home slash line .258/.326/.408
Road slash line .252/.315/.391

Those difference might not seem like a lot, but remember that they are essentially park neutral since they include home and road games in all the parks, plus each split includes more than 90,000 plate appearances. A difference of 6 batting average points is more than 500 hits over than many PAs.

There's also a huge advantage in home runs for the home team. In 2011, home teams averaged 1 homer every 39.4 plate appearances. Road teams averaged 1 homer every 42.1 plate appearances.

Why is there such an advantage in hitting at home? There are two likely reasons:

1. Home teams are, on average, more rested than visiting teams. Not only are the players sleeping in their own beds, but if you look at the first game of the second series of a homestand, the visiting team has just traveled from somewhere and the home team hasn't. This is, of course, why teams usually send starting pitchers ahead to road starts, so that they aren't traveling the night before.

2. Home teams face the opposing pitcher's closer a little less often. When the game is tied, the visiting team is more likely to hold their closer until they have a lead. For example, if the game goes to the 9th inning inning tied and the visiting team doesn't score in the top of the 9th, they are likely to hold their closer out in the hopes that the home team doesn't score in the bottom of the 9th but they are able to go ahead in the top of the 10th and use their closer in the bottom of the frame. If, instead, the home team walks off with the victory in the bottom of the 9th, then the visiting closer never gets into the game. Closer consistently have the best average against numbers in baseball, so subtracting a fraction of their appearances helps the home team stat lines.

It's also interesting to look at the home team winning percentage (regular season) historically:

The red line is the actual value for each year while the black line is the average of the last 5 years. A couple of things stand right out:

  • 2011 saw a huge drop in home team win percentage to just .526. There are just 11 years since 1919 with a lower home team winning percentage.
  • Other than 2011 itself, the percentage seems to trend with offense. That makes sense--as homers flew out of parks in the mid 1990s, for example, being at home was less of an advantage. As offense has dropped off throughout the 2000s, the home team won more and more until this past season.
Anyway--that's the story with home/road splits. More to come in the next couple of days.

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