IntroductionHome advantage (HA) is a term coined to describe the consistent finding that home teams win over 50% of the games played under a balanced home and away schedule in sport competitions 1,2,3,4,5 . This is a well-documented concept in a wide range of team sports 5,6,7 and, in football (soccer), it has been verified since the inaugural season of the England League in 1888 5,8,9,10 .The HA occurrence has been justified by previous authors due to extrinsic and intrinsic factors. The extrinsic factors are game location 11 , weather 12 , crowd effects 13,14,15 , travel length 3,13,15,16,17 , and referee bias 14,15,17,18,19 28 . However, the findings cited above considered only the single-leg HA that ideally regard a balanced playing schedule in which each team plays each other team the same number of games at home and away. Therefore, there a lack of data about the second-leg HA concept which is relevant in all two-stage knockout competitions and occurs when, on average, teams are more likely to pass a two-matches knockout stage when playing the second-leg at home, i.e., even though both teams have an HA since they play one match at home, the advantage is greater for the team that plays the second match at home 29 .To the best of our knowledge, only four studies have investigated the second-leg HA. However, they were based on European tournaments and present conflicting conclusions because second-leg HA varied from 61.8% (with second-leg HA) to 47.8% (no second-leg HA) 20,29,30,31 . These differences may be explained due to the different mathematical models used to access second-leg HA. For example, Eugster, Gertheiss, Kaiser 30 , using the naive analysis, found a probability of winning in favour of the team having the return match at home (56%). However, using refined statistical data analysis -which considered the team coefficient proposed by the UEFA -the authors suggested no evidence for the second-leg HA 30 . Lidor, Bar-Eli, Arnon, Bar-Eli 31 , using multiple χ 2 analyses, also suggested that teams which play the second game at home have a substantially higher chance of advancing to the next round than teams playing the first game at home. On the other hand, using a regression model and discriminant analysis, García-Rubio, Gómez, Lago-Peñas, Ibáñez 20 found no effect on the success Methods: A naive analysis was applied considering how many times a team that played the second leg at home qualified for the next round. To verify differences between home, away and draw results, the Chi-square (χ 2 ) and the Full Bayesian Significance Test were applied. For the binomial variables ("Home" or "Away"), the probability of secondleg knockout occurrence was calculated. Results: The probability of second-leg HA varied from 27.27% to 63.64% suggesting fluctuations of second-leg HA during competitive phases (round of 16, quarterfinals, semi-finals and final matches) and decision forms (full time, goals away rule or penalty-shoots). Conclusion: The results counteract the common belief that there is a large advantage ...