Home Field Advantage

At a lazy pace, I've been reading chapters of Scorecasting: The Hidden Influences Behind How Sports Are Played and Games Are Won by Tobias Moskowitz and L. Jon Wertheim. The book was marketed as Freakonomics for sports fans and there is a lot of truth in that description. The authors use tools of behavioral economics and apply them to various sports-related questions.

For example, a couple of interesting middle chapters try to determine the cause of home field advantage. The authors use various measures to demonstrate that players perform at about the same level in home versus road games; yet, every major sport has some level of home field advantage. This summary is from a presentation Moskowitz delivered for a conference:

"Home field advantage exists in every sport, at all times in history, and in all geographies," said Moskowitz, Fama Family Professor of Finance. 

"And it's remarkably consistent," he added, citing statistics from the five most popular team sports—football, basketball, baseball, soccer, and hockey. In basketball, for example, both NBA and WNBA teams win about two-thirds of the games that they host. In baseball, the home team prevails roughly 54 percent of the time, whether it's an MLB game or played in Japan.

In addition to the consistency of player performance in different venues, they similarly dismiss other possible causes of the advantage, including fan enthusiasm (at least not the conventional interpretation) and travel. Basically, Moskowitz and Wertheim find that referee/umpire behavior is at the root of a significant portion of home field advantage.

"We don't think this is conscious," said Moskowitz, who built on previous studies of soccer referee bias to uncover the connection to home field advantage. The cause, he says, is physchological [sic], and in particular, related to social conformity. 

"Basically, what's happening is referees start to see things the home crowd's way," Moskowitz explained. 

In high-stakes game situations before making a split-second decision, referees seek both information from fans—and their approval. 

I am especially interested in baseball and their results ostensibily explain much of the home field advantage in my favorite sport:

Referee bias becomes more evident, Moskowitz said, as the calls become more ambiguous—borderline strikes in baseball, for instance—and as crowds become more animated and opinionated. 

Fear of blowing a call can cause referees to look for ways to "relieve some of that presure," Moskowitz said, "of having 50,000 screaming fans yell at you." 

And the calls affect the scoreboard. In baseball, Moskowitz examined the strikezone and estimated that visiting teams receive 516 more strikeouts and are issued 195 fewer walks from home plate umpires over the course of a season.

"If you add up how much this is worth in terms of runs scored and everything else, that can explain a sizeable chunk of the home field advantage in baseball," said Moskowitz.

Spoiler alert: the book presents evidence finding that umpire bias disappeared in baseball games in stadiums that major league baseball had rigged to use QuesTec to evaluate umpire performance. Actually, umpire bias didn't disappear -- it moved in the opposite direction and created a substantial road team bias on ball-strike calls. They refer to this evidence as the "smoking gun" and find that other indicators of home field bias did not shift since Ques Tec was only monitoring ball-strike calls at home plate.

However, to me this finding completely deflates the psychological conformity thesis. Umpires must have known about the data finding home field ball-strike bias and then intentionally changed their behavior to correct for the problem. This makes the result conscious.

A few years ago, a study found that umpires were slightly more favorable calling balls and strikes for pitchers of their same race. Again, however, the presence of QuesTec eliminated this bias.

The chapter made me think about other situations that could be compared. If scrutiny from QuesTec diminished umpire bias, what about the extra scrutiny of post-season play in the instant replay era? Does Tim McCarver's commentary work to decrease umpire bias? What about the possible differences in highly scrutinized televised games during the regular season versus obscure games played without so many viewers? The Yankees and Red Sox play many more TV games than do the Royals and Pirates.

If home field noise provides pressure to influence umpires, is there more bias in years when small market teams draw sizeable crowds? How about a study of bias in Twins games during years when the team draws about 1 million fans versus the years when they draw 3 million?

Phil Birnbaum has a strong critique worth reading.


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