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In football during two-legged ties there exists a phenomenon called "second leg home advantage". Many managers, players and commentators believe that if the second match of a tie is played on one team's field then they have slightly better chances to win the tie.

UEFA also believes in this phenomenon, because e.g in the round of 16 of the Champions League the teams winning their group stages are playing their second game against group runners-up at home, so that group winners have more chances to win the tie.

So, the question is, does the second leg home advantage phenomenon exist and is it statistically justified?

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    I've posted this as Q&A and you are very welcome to improve the answer or post another one. – gdrt Apr 15 '17 at 10:12
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This question has been addressed in the paper by Lionel Page and Katie Page (2007) 'The second leg home advantage: Evidence from European football cup competitions', Journal of Sports Sciences, 25: 14, 1547 — 1556.

The researchers statistically analyzed 12,364 individual matches from the following competitions:

  • UEFA Champions League (1955 - 2006)
  • UEFA Cup (previously InterCities Fairs Cup, now Europa League, 1955 - 2006)
  • Cup Winners Cup (1955 - 1971)

In order to reduce the effects of the UEFA seeding system allocating the "better" teams as the second leg home team, the UEFA club coefficients were taken into account in calculations of the probability of the second leg home team winning the tie. The results were as follows:

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| Tie-breaker | Prob. of SLHT* winning the tie | Number of ties |
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|    None     |             53.77%             |      5750      |
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| Extra time  |             66.42%             |      186       |
-----------------------------------------------------------------
|  Penalties  |             57.33%             |      148       |
-----------------------------------------------------------------
|   Overall   |             54.33%             |      6084      |
-----------------------------------------------------------------

*SLHT - Second leg home team

The probabilities above show us that SLHTs have slightly better chances for winning the tie, but the following chart illustrates how these probabilities (considering only the ties without tie-breakers) decreased over time since the beginning of the aforementioned competitions.

Lionel Page and Katie Page (2007) 'The second leg home advantage: Evidence from European football cup competitions', Journal of Sports Sciences, 25: 14, 1547 — 1556Source

What this paper shows us is that there is a very small second leg home advantage in the ties decided without tie-breakers and a significant advantage in the ties where tie-breakers were used.


There was also another research by Manuel J.A. Eugster, Jan Gertheiss & Sebastian Kaiser (2010) LMU Munich 'Having the Second Leg At Home – Advantage in the UEFA Champions League Knockout Phase?', where they analyzed only 304 individual matches from the UEFA Champions League (1994 - 2010) also using UEFA club coefficients for removing seeding system disturbance and they concluded that:

There is no statistical evidence for the common belief that the chance of winning is higher if a team is playing away in the first leg and having the second leg at home.

Moreover, they have proposed:

to change UEFA regulations in the sense that in the round of 16 group winners do not automatically play at home in the second leg, but may choose depending on their individual preferences.


But, why people do believe in this phenomenon despite poor statistical evidences?

Well, perhaps, because when the tied teams are equal they choose "defend away, win at home" strategy, and mainly because of the away goals rule. Probably, the general reasoning, as Patrick Kluivert stated, is that:

Sometimes people make mistakes and it is better to make your mistakes in the first leg away from home because there is still time to put things right in the second match.

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One potential advantage is that they know that if they can get one or more away goals and keep the score level or only down by one they can advance either with a scoreless draw and park the bus or by only scoring one goal and then parking the bus. Another advantage would be that if the tie went to extra time the 3o minutes of extra time would be played at their ground, and therefore they would have an extra 30 minutes at home.

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I crunched the numbers on Word Cup intercontinental playoffs. The team that plays the 2nd leg at home has won 61% of the time as per bitedge.com.

I think it's because in the 2nd leg you know exactly what result you need and you have a greater chance of determining the result at home than you would away.

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    16 (7 vs 9) samples with such a high entropy are never enough for almost any statistical study. It was a nice thing to know, but I am afraid it doesn't qualify as an answer for the original question. – gdrt Sep 10 '17 at 13:21

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