By Chris Stokel-Walker

Football teams appear to retain an advantage over opponents when playing at home despite there being no fans in the stadium – puzzling those who thought the home crowd helped player performance.

In European football leagues, historical analysis of games shows the home team wins around 50 per cent of matches, with the chance of a draw or home defeat both standing at around 25 per cent. The home advantage has been theorised to be caused by the roar from the crowd geeing up the home players – and possibly intimidating the referee in a way that encourages them to give decisions advantageous to the home team.

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The closure of sports stadiums to fans during the coronavirus pandemic gave Daniel Memmert and his colleagues at the German Sport University Cologne the chance to test these ideas. They looked at data from 40,000 men’s football matches before and after the banning of fans from sports events, including more than 1000 held behind closed doors across Europe.

The researchers found that the referee’s bias towards the home team disappeared in the games played during lockdown, with fewer yellow and red cards given to away teams than in games played in front of fans. But the proportion of away teams winning matches played without fans increased just 7 percentage points across Europe, which Memmert says falls below the level of statistical significance.

“We think territorial behaviour could be one factor for the home advantage,” says Memmert, comparing it to children being more dominant and outgoing in their own homes, and more reserved when visiting a friend’s house.

There were differences by country. In the English Premier League, the likelihood of home teams winning, losing or drawing barely changed, while in the German Bundesliga, home teams were 15 percentage points more likely to lose during the pandemic.

The findings are “striking”, says Joey O’Brien at the University of Limerick, Ireland. But he cautions against using them to draw firm conclusions. “The data used was in the later stages of most of these leagues,” he says: some games at this stage may be less competitive because the teams they feature are safe from relegation, but also not challenging for the league’s top spots.

Yet as sport carries on behind closed doors, the availability of almost an entire season of data without spectators will firm up the hypotheses, says O’Brien.

Journal reference: PLoS One, DOI: 10.1371/journal.pone.0248590