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Statistically Speaking: Homefield Advantage and Overtime

Wednesday, July 16, 2014

Homefield Advantage and Overtime

Last week, I examined homefield advantage and tried to determine which teams benefited the most from playing at home versus playing on the road. This week, I want to explore another aspect of homefield advantage.

According to a study, located here, homefield advantage dissipates over time. No, this doesn’t mean that the Boston Red Sox and Chicago Cubs should move out of their 100 year old stadiums if they want to win more home games. It means that homefield advantage is strongest earlier in games. In other words, the home team benefits the most from homefield advantage (increased adrenaline, benefit of calls, increased nervousness for their opponent, disruptive crowd noise, and a host of other dynamics that may or may not be contributing factors) early in games and as time elapses, the homefield advantage lessens. To test if this phenomenon is true, I looked at every overtime game in IA (or FBS) college football since 2005 that was a non-neutral site affair (i.e. one team was playing at home). I then simply looked to see if the home team won or lost the overtime game. In 287 overtime games, the home team won just 142. Their overall record was 142-145. For the non-statistically inclined, that means home teams won just over 49% of the time (.4948 win percentage), which is of course, less than half. So there seems to be a great deal of merit to the idea that home field advantage dissipates over the course of a game.

Before we leave this issue, I want to delve a little further and look at the betting favorite in the overtime game. Thanks to the great Phil Steele and his college football annual, I have historic point spread data and can determine which team was favored by the Vegas oddsmakers to win each game before it started. My friends, this is where things start to get interesting. The home team was favored in 194 of the overtime games. They won 106 of them (I did not check to see if they covered the point spread as this was not the intent of the study). The 106-88 record works out to a winning percentage of .5464 meaning if the home team was favored, they won in overtime nearly 55% of the time. Now, what about the other side of the coin? If the home team was an underdog, as they were in 91 instances, they won only 36 times. The 36-55 record works out to a winning percentage of .3956, meaning home underdogs won overtime games under 40% of the time. Astute observers will note that 194 and 91 do not add up to the 287 observations mentioned in the previous paragraph. That is because on two occasions, the home team was even money to win against the team they were hosting. The home team lost both of those, but we can’t draw a great deal of conclusions from a sample size of two.

The biggest takeaway from this study is that the point spread does a bettor (pun alert) job of picking the winner of overtime games than the venue. Head coaches might do well to keep this bit of information in mind when deciding whether to play for overtime or attempt to win in regulation. The notion of playing for overtime at home should be weighed against the quality of the opponent (as indicated in the point spread of the game) in determining the correct course of action. A prime example of a head coaches’ understanding of this notion comes from Brady Hoke’s decision to go for two against Ohio State after a late score in last year’s game. The Buckeyes came in as a 16-point favorite over Hoke’s Wolverines, so even though the game was in Ann Arbor, the two point call was a smart play.

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