The Value of Home Field Advantage
by Trevor Whenham - 12/23/2006
Of all the factors that go into handicapping, few get mentioned, discussed, overcompensated, undercompensated or ignored more than the advantage of playing at home. If you do enough reading and you talk to enough people then you will become thoroughly confused about the importance of home field advantage, the value that should be assigned to it, and the best wagering strategies to deal with it.
If we're going to look at home field advantage, we should start with the big time - the NFL. It is generally accepted that the NFL home field is worth three points. That is to say that if two perfectly matched teams were to play then the home team should be favored to win by a field goal. That's a generalization, and like all generalizations it is somewhat accurate but potentially very dangerous. Though a recent four-year study of the home field showed an average of about three points, the effect of the home field advantage actually changed significantly from week to week.
For the first 12 weeks of the season the average value of the home field advantage was 1.3 points. For the last five weeks, that average jumped all the way to 5.3 points. That jump can be explained by a number of factors, including fatigue as the season continues, teams being eliminated from playoff contention and playing younger or inexperienced players, injuries, and more established consistency after teams have played for three months. What it shows is that the standard three-point assumption would cause us to overcompensate for home field advantage early in the season, but then not give it enough credit later in the year. In both cases it could cause handicappers to accept spreads that may not actually be appropriate.
Figuring home field advantage in college football creates an extra layer of difficulty. Not only do you have to assess in the factors that we mentioned above, but you have to consider that the players are younger and less experienced, the season is shorter, the pressure is higher because of the huge significance of a loss and the size of the crowds are very different. Clearly the impact of playing in front of 110,000 at Michigan will be more significant than playing in front of 10,000 in Buffalo. As a result, using a single home field adjuster in college football can be especially dangerous. The proper impact of home field in a given week could range anywhere from 1.5 points to as many as 5, according to the bookmakers at Bodog.
The advantage of playing on the home court in basketball also provides differences between college and the pros. Bodog generally puts the value of the home court between 3.5 and four points in the NBA. In college, the value can change dramatically depending upon the court and the school involved. Gonzaga, with its incredible home winning streak, or Duke with the Cameron Crazies, are much tougher places to visit than schools that haven't had success and don't draw significant or vocal crowds. Calculating in the impact of home court in the NBA adds another twist.
"Distance can play a role especially on the tail end of a long road trip as the fatigue sets in," said a Bodog oddsmaker. "For example, a key ingredient in the NBA is not so much the home court, but the travel associated with getting to that court." That means that the Lakers would get more value from eating home cooking if the Raptors were visiting them on the ninth day of a western swing than they would if the Warriors dropped down for a home-and-home series.
Establishing a value for home field in Major League Baseball is challenging for a number of reasons. Between the lower scores, the larger number of games and the fact that teams get to settle into a city for a few days instead of having to travel between every game, the impact of the home field is small. Between 1991 and 2002 the home field was shown to give the home team 2.84 more wins per season than they would have had on neutral fields. That's not particularly relevant over 162 games. It's also worth noting that the historical trend of the home field advantage is that the impact is decreasing, likely due in large part to the easier travel and the shorter home stands that teams face.
What impact does home field have on lines? Depending on who is playing, it can be significant. "Bettors will tend to overcompensate with home-field or home-court advantage if it is a public team playing at home," said the Bodog oddsmaker. Given the general public enthusiasm for favorites, that makes sense. The line will already have the home field factored in, but bettors will credit the home crowd, and will often run that line higher than would otherwise be warranted. That means that value can be present in these games, and can explain some of the appeal of road underdogs. On the other hand, with an unpopular home underdog, the public can be drawn more enthusiastically to the favorite because the spread will appear to be a value because the home field advantage will be factored in. In these situations, the public's lust can create value for the home team.
Bodog points out that the public will compensate for home field differently based on the performance of the teams involved. "For example, if a team is 22-1 ATS at home, bettors are going to continue to jump on the bandwagon and ride the winning record," said the bookie. "On the other hand, if they play better on the road, bettors will put less weight on home court when making their decisions." An interesting example of this is the Calgary Flames. They have won their last ten games on home ice, and they just recently broke a simultaneous five-game losing streak away from home. In both cases, those trends would likely be strong enough for bettors to overvalue the impact of home ice for the hosts.