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Wednesday, August 15, 2012

Finding home field advantage: field goals

Can a home crowd rattle a visiting kicker?

To me, home field advantage is a fascinating topic. I assume that's because I grew up attending games in the best home environment in college football. On average, home teams get a 3 to 3.5 point boost from playing in their own stadium. Some teams get moreI've argued before that this is more a product of (1) the travel required to get to these stadiums and (2) the hostility of the crowd (in that order) than the number of people in attendance. Getting to Lubbock, Boise, Lincoln or College Station takes something out of a team. Appalachian State found last year that it's harder to go into Lane Stadium than the Big House.

But how does home field advantage actually play out? Are home teams better in every way, or do they enjoy advantages in specific aspects of the game? If the crowd motivates the home team, we would expect better play in pressure situations and in extending momentum. If the crowd disrupts the road team, we would expect more false starts, turnovers and other miscues, or the road team might be more conservative in their play calling to avoid mistakes. If travel leads to fatigue we would anticipate better play from the home team late in games and more explosive plays. Where, exactly, do those extra 3 points come from?

My challenge is to find a definitive answer using the available statistics. I begin with this: over the last three seasons, home teams in conference games have scored 28.576 points per game while road teams have scored 25.425 for an average margin of victory of 3.151. By looking only at conference games, I can rule out any correlation between playing at home and any other quality that might influence play because, in the appropriate technical parlance, location is randomly assigned*. So, I need to explain where those 3.151 points come from. Fortunately for me, I have a bag full of tricks for assigning point value to events in football games.

I begin today with field goals. First, are home teams more likely to make field goals? Second, is that advantage larger in pressure situations? 

In answer to the first question, in 1,350 conference games (at non-neutral locations), home teams have attempted 2,107 field goals, connecting on 74.1%, and road teams attempted 2,021, hitting 71.4%. Removing the advantage that allowed home teams to kick more field goals (something I'll look at another day), that gap in accuracy is worth .121 points per game or about 3.84% of the home field advantage. Using the KPOE method I discussed earlier, home teams enjoy a .122 point advantage per game from greater field goal accuracy.

What about pressure situations? I looked only at kicks in the 4th quarter in which the field goal could put the kicking team within a touchdown, give the kicking team a lead greater than a touchdown, or anything in between. In these situations, the home team enjoyed a .261 point advantage per kick, more than three times larger than the .082 point advantage per kick for home teams for all field goals. (Both home and road kickers are substantially worse in pressure situations.)

Net net, home teams have a clear advantage when kicking field goals. That advantage increases with leverage (leverage being the degree of influence that kick has on the final outcome of the game). While the former could possibly reflect a familiarity with the field and field conditions, the latter is undoubtedly a result of the crowd rattling (or failing to comfort) the road kicker when the heat was on. So yelling at the opposing team's kicker does help, but, at .121 points per game, rarely affects the outcome; kicks can sail wide right in Tallahassee just as they can in Miami.

*In non-conference games, teams from bigger programs are more likely to host teams from smaller programs. Usually, teams from bigger programs are better - though Georgia discovered last season that this is not always true. This makes it hard or impossible to scientifically analyze home field advantage in non-conference games.

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