The field factor and the referee’s influence

The referees award almost the same fouls to home teams as to away ones, but away players are sent off more easily

Finished the previous post telling about one of my reference books here in this blog: Scorecasting: The hidden influences behind how sports are played and games are won. One of the studies that the book mentions was made by two Spanish economists that in 2005 set out to see how peer pressure affects human decisions. Luis Garicano and Ignacio Palacios-Huerta counted the extra minutes added by referees in the Spanish league, taking into account the result of the score in the 90th minute.

In most cases, the referees added about three minutes on average, but when the difference was only by one goal there was a clear deviation: if the home team was winning, the average went down to about two minutes. On the contrary, if the away team had an advantage of one goal, the average of extra minutes added went up to four.

Illustration: Idoia Vallverdú
Illustration: Idoia Vallverdú

To learn a bit more about this, we have analysed how many fouls per game have been awarded to home teams and away teams in the last ten years, and also how many yellow and red cards have been shown.

The result is that in the overall of the five leagues 2.6% more fouls are awarded to away teams than to home teams, but in some countries home teams are the ones that are awarded more fouls. The difference, however, soars according to the gravity of the sanction: away teams see 20% more yellow cards than home teams, and up to almost 42% more red cards. It is true that while the referees blow for more than 10,000 fouls per season, they only show 100 red cards, making it easier in this regard for the differences in percentage to be higher. But looking at the figures, it is not nonsense to think that the referees favour more home teams the more difficult the decision they have to take is.

The field factor and the referee's influence

Less fouls, same cards

From the statistics of these ten seasons other curious facts can be drawn: the number of fouls awarded has dropped self-evidently in every league, and specifically in the Spanish league it has dropped from almost 15,000 in the 2005-2006 season to less than 11,000 per season for the last three years. Overall in the five major leagues in ten years, referees have gone from blowing for 35 fouls per game to about 28. The evolution is very similar in four of the five competitions, but in English football is quite different, and the data clearly confirms one of the classic stereotypes of the European football: English football is clearly where the referees give more freedom to play. But also in this aspect there is a trend towards standardization since ten years ago in England referees awarded about 13 fouls less per game than in other leagues, and in the last two season the difference has stood at around 7.

Average fouls signalled per game

This clear and continuous decline in the number of fouls awarded per game has not been accompanied by a decline in the number of yellow cards: in general, about 4 per game are shown, a figure that has hardly changed in the last 10 years. The Spanish league is where more cards are shown (5.2 per game) and in England where less (3.2). What we can see is a slight drop in the number of players sent off, but the trend is nowhere near as remarkable as the number of fouls. On average in the five competitions a total of 0.25 red cards per game are shown, that is there is a player sent off in every 4 games. It is also in this aspect that Spain leads in the card tally, since a player is sent off by the referees every 263 minutes on average, whereas in England a player leaves the pitch every 518 minutes.

Playing at home is no longer the advantage it used to be

A study of every match of the 5 most important European football leagues since 1970 up to nowadays. Overall, at the end of the 70’s teams retained almost 70% of home points, whereas in the last seasons this figure has come down even below 60%

To start this blog site I get back an article I published on the newspaper ARA on august 2015. A study about the scores of the 5 main European football leagues, based on a database I made up using datasets from I’ve split it into two halves. Here comes the first one:

Everyone knows that playing at home is a way to start the match with an advantage, but to what extent playing a game at your home stadium favours a team? To be able to appreciate the importance of the field factor we have analysed the results of all the matches of the five major European football leagues from 1970 to the present, and the overall answer is that in all these years, home teams have won 64.5% of the points and away teams, 35.5%. That is, home teams have managed to secure almost 2 out of every 3 points they have obtained. There are differences between countries that are never higher than 5 percentage points. France is where teams retain more points at home (67%), whereas in England is where they get less (62%). One of the first questions hanging in the air is whether or not the fact that in English matches visiting supporters usually occupy a significant part of the stadium can be related to this difference.

The decline of the home teams advantage in football

If we chop up the figures by season, we find something we were expecting: the field advantage today is no longer what it used to be in the previous decades, and it is important to note that it has been going down over the last seasons. Overall, at the end of the 70’s teams retained almost 70% of home points, whereas in the last seasons this figure has come down even below 60%. Another thing that is obvious by looking at the first chart that accompanies this piece is that over the years the lines of the different countries have been getting closer, that is during the last seasons the differences between leagues have narrowed.

These figures alone don’t provide any evidence, but probably most readers of this article will share the hypothesis that the gradual pacification of the stadiums over the years seems to have been a key factor in explaining this sustained trend. It is easy to think that the lower the level of violence in a stadium is, the more relaxed away players play and the less pressure referees feel when blowing for fouls, and that all of these help to balance the scale between the teams. On this basis, it is interesting to look at the chart for the figure of the final of the European Cup in 1985 between Liverpool and Juventus, played at the Heysel stadium in Brussels. The fights between fans before the match ended up with 39 supporters (most of them Italians) killed and around 600 injured. For the significance of the match, this is probably the biggest tragedy in a European football stadium due to fights between supporters. Interestingly, during the years after the Heysel disaster it is in the English football league where more teams fail to win at home, but in general the downward trend accentuates over the next decade.

Illustration: Idoia Vallverdú

There is one last aspect that is striking in the chart: the country and the period in which winning away is more complicated is in Spain during the transition. There is a clear peak around the year of general Franco’s death, and that has to make one consider whether or not a period of social upheaval and instability like that one could have had an indirect influence on the fact that home victories were easier.

So far we have been talking about violence, but if we asked ourselves why is it easier for teams to win at home, probably most of us would reply that it is due to a mix of the effects of the public on the players and referees, the difference in size or the grass that may exist between one stadium and another, or even perhaps we would add the weather. 4 years ago, the journalist Jon Wertheim and the economist Tobias Moskowitz resolved themselves to clarify precisely the reasons behind the field factor in their book Scorecasting: The hidden influences behind how sports are played and games are won. From the statistical analysis of different data sets in various sports they came to the conclusion that the responsibility falls primarily on the referees. According to them, nor weather, nor traveling, nor fields affect the results, and even the effect of the supporters on the away team is not significant. Actually, that’s what the next post will talk about.

What if we take Barça and Madrid of the league

NOTE: A reader comment when the article was published suggested that the drop on the home field advantage in the Spanish football could be related to the increasing gap between the two main teams (Barça and Madrid) and the rest. That was easy to check, filtering all the games on which Barça and Madrid are involved, and so getting a league without them. The result is a very similar graph, without Barça nor Madrid, the home field advantage would have also declined. On the comments I was also asked about the change from 2 to 3 points per win, I indeed took this into consideration, as well as paid attention to the difference in the year it was applied.