With SBR's new editorial series, 'The Psychology of Betting', Joeseph Buchdal will be diving deep into the various aspects of sportsbetting to demystify betting strategies, concepts and what we often consider rules of thumb.
In many team sports it is typically observed that the team playing at home holds an advantage over the visiting team, winning significantly more games than their opposition. My data set of NBA results dating back to 2009 shows 59% of games were won by the home team. In their book Scorecasting, Toby Moskowitz and Jon Wertheim report a home win rate of 57% in football since the inaugural Superbowl season in 1966. They similarly report home-field advantages in NHL (59%), international cricket (60%) and rugby (58%). Since the inception of the English Premiership 1992, home teams have won close to twice as much (46% of games) as away teams (26%). Even in Major League Baseball, where luck arguably plays the greatest role, 53% of home teams win their games. The question is why?
Fans & Familiarity
The most commonly cited explanations for home-field advantage are the influence of fans and the familiarity of playing on the home ground. Typically home fans vastly outnumber away fans; the home team can expect to receive vociferous support whilst the away team may be heckled and booed. Football and baseball teams whose stadia are domed, and therefore noisier, appear to have an increased home advantage. Players at home will also be more spatially familiar with their ground, pitch size and playing surface allowing them to build up a database of visual cues which can be recalled more intuitively than when playing away in less familiar surroundings. Furthermore, whilst the away team may have to travel a significant distance to the game, players for the home team will have access to all their usual creature comforts. According to this hypothesis, home-field advantage should diminish where home and away teams come from the same city. Evidence from derby games like Lakers versus Clippers (NBA) or Rangers versus Islanders (NHL), however, suggest that it doesn’t.
Whilst Moskowitz and Wertheim have ruled out explanations of crowd support and home familiarity for home-field advantage, the soccer blogger and analyst Mark Taylor has investigated what happens to home performance when a soccer teams relocates to a new stadium. The Premier League team Tottenham Hotspur is the latest to switch venues to Wembley whilst a new stadium is built after White Hart Lane was demolished at the end of the 2016/17 season. Over the past couple of decades 27 teams have undergone similar moves, usually permanent ones to new stadia. Measuring home-field advantage by average goal superiority over a season, Taylor looked at how these 27 teams collectively performed relative to the league benchmark. Three and two seasons prior to their move these teams were performing in line with their league average. In the final season before relocation, home-field advantage increased by 22% relative to the benchmark. In the first season at the new ground, however, home performance dipped 12% below the benchmark, and by season three had still not completely recovered.
Moskowitz and Wertheim were clear that whilst crowds have little influence on home performance, referees, by contrast, could be easily influenced by them, albeit involuntarily, documenting examples of official bias at crucial times in baseball, football, hockey and basketball. Ryan Boyko has even gone as far as to propose an equation relating crowd size (and by extension the strength of influence on the referee) and home-field advantage in the English Premier League: for every extra 10,000 people in the crowd, the advantage for the home team increases by 0.1 goals. Of course, better Premier League teams tend to have bigger stadia with bigger home crowds. Being superior they also tend to have more of the attacking play in potential goal scoring situations. Consequently, the enhanced home-field advantage might simply be a product of having better players. Ryan also demonstrated that home teams were awarded more penalties and fewer bookings. Yet the direction of causality is unclear: does enhanced attacking performance through home-field advantage cause referees to award more favorable decisions to the home team, or does referee bias actually cause some of the home-field advantage?
Testosterone & Territoriality
Nick Neave and Sandy Wolfson have proposed that a protective response to an invasion of one’s perceived territory – or territoriality – may provide a hormonal explanation for home-field advantage. Specifically, they found that salivary testosterone levels in soccer players were significantly higher before a home game than an away game. They also found that testosterone levels were higher the greater the perceived rivalry with the opposing team. Justin Carré has reported similar findings for both salivary testosterone and cortisol (a stress hormone) in elite hockey players.
Intriguingly, an evolutionary adaptation to protecting territory may also manifest itself as an aversion to losing. In his best seller Thinking, Fast and Slow, Nobel Laureate Daniel Kahneman popularises his ground breaking body of work with colleague Amos Tversky identifying the cognitive psychological biases that all of us are prone to. Prime amongst these is loss aversion, a tendency to prefer avoiding losses relative to acquiring equivalent gains, something that every gambler is probably very familiar with. Some studies have suggested that the pain of losing is about twice as powerful as the pleasure of gaining.
A lovely demonstration of our aversion to losses has been found in the world of professional golf. Studying over two and half million putts from the PGA Tour between 2004 and 2009, Devin Pope and Maurice Schweitzer observed that a disproportionate number of those for par were completed compared with attempts for birdie. Of course, a putt for making birdie is invariably a trickier proposition than that for saving par – it’s usually much longer. Nevertheless, even after accounting for the effects of distance, the golfers still putted 3.7% more shots for par than for birdies. Pope and Schweitzer speculated that the reason was loss aversion. Making birdie is considered a gain, understandably so because it is one shot better than what the golfer should be achieving. Similarly, shooting a bogey will psychologically be seen as a loss. Given what Kahneman and Tversky have taught us about loss aversion, these findings were probably inevitable.
We might speculate that loss aversion accounts for some of the home-field advantage seen in team sports. From a psychological perspective, points dropped at home will be experienced as a loss, whilst points gained away from home will be seen as a gain. Since we are more sensitised to avoiding losses than receiving gains, the home team will, on average, try harder than their opposition. Of course, loss aversion won’t necessarily explain why home teams should feel that dropping points at home should hurt more than dropping points away, although saving face in front of your fans might have something to do with it. Indeed, Mark Koyama and J. James Reade have proposed that soccer players are motivated to perform better when they are monitored by their fans. Since there are more fans watching when they play at home, players will try harder at home than when playing away. Further, Koyama and Reade have argued that, since television serves as a “monitoring technology” enabling away fans to monitor their team’s performance more easily, the increase in televised soccer may have contributed to some of the decline in home-field advantage in English professional soccer over the past century.