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.
