How important is being at home for the second leg?

How important is being at home for the second leg?

By Jack Ratcliffe Feb 6, 2013

Tweet

Whenever there’s a Champions League knockout draw, both fans and pundits instinctively do the same thing: check to see which sides are at home for the second legs. But is the second-leg advantage simply a misconception?

In the Champions League there is a strongly held belief that the team playing their second leg at home has a huge advantage over their rivals. It’s easy to see how this myth started when you consider that, out of 152 Champions League ties between 1994/95 and 2009/10, the team allowed to play the second leg at home progressed to the next stage 85 times.

That’s an estimated probability of 56% that the return-leg home side will progress – a margin significant enough to influence anyone’s Champions League betting.

Destroying the Myth

Unfortunately, like most myths, this is wildly inaccurate when placed under scrutiny. The result above completely ignores how Champions League second round ties are created.

In the second round, the teams that play at home in the second leg are always the group winners. This means that most favourites get to play at home in the second leg. By placing most (if not all) of the favourites in one place, the average is skewed to the 56% we saw earlier.

For example, imagine if you moved Real Madrid, Barcelona, Juventus, Bayern Munich and Chelsea to the north of England. Would you say that the north of England produced the best football teams? No – you would simply notice that the best teams have moved up north, and that the area has no impact.

A simple way to remove this bias is to eliminate second-round ties from the data. The later rounds no longer guarantee that the favourites will play at home in the second leg, and therefore this can more fairly determine how often the side with a return match at home progresses.

So how often do the teams playing their second leg at home – excluding the second round – progress? Exactly 50% of the time.

Send in the Statisticians

Things get even more damning for the home-team theory when you examine the work of statisticians Manuel Eugster, Jan Gertheiss and Sebastian Kaiser, who researched the subject in 2010.

Their frequency table (displayed below) showed that on the 22 occasions when a group winner met another group winner in the knockout stages, it didn’t matter who played the second leg at home. Both home and away sides won 11 times – exactly 50%.

The frequency table also highlighted two other interesting trends:

> On the nine occasions when a runner-up met another runner-up, the team playing at home in the second leg actually triumphed just 33.3% of the time.

> When group winners played the second leg away to group runners-up, the progression rate was just 50%.

These points contradict each other. The first one suggests that teams actually do better when playing away in the second leg, as more runner-up teams progressed. The second point suggests that group runner-ups can win equally as many as group winners, if the runner-up has the second leg at home.

As the above statements are mutually exclusive, and therefore both can’t be true, there must be other factors at work. The most obvious reason for these anomalies is the difference in the ability of teams who finish runner-up.

For example, runners-up in difficult groups are usually of a much higher standard than those in “soft” groups. This year Real Madrid, Manchester City, Borussia Dortmund and Ajax – all domestic league winners – were placed in a group together, you’d expect the runner-up to do exceedingly well in the competition.

Refining the Data

Eugster, Gertheiss and Kaiser also noticed that there can be marked differences in the quality of group winners and runner-ups, and so refined their data by using UEFA coefficients, which use a club’s last five seasons of European form, rather than just the six games of the group stages.

The statisticians coupled this with what is known as a logistic regression model (click here to see their calculations), to prove that the better teams progressed whether or not they played the second leg at home or away.

They also noted that teams of a very similar ability progressed an equal number of times whether they were at home or away. Therefore there was absolutely no advantage in playing the second leg at home – despite what television pundits might suggest.

*Odds subject to change

If you have feedback, comments or questions regarding this article, please contact the author.