What is a good result in the first leg of a two-legged football match?

The most important pan-European football tournaments include ties where two clubs play each other over two matches and the aggregate score determines which is admitted to the next stage of the competition. A number of stakeholders may be interested in assessing the chances of progression for either of the clubs once the score of the first match (leg) is known. The paper asks what would be a “good” result for a team in the first leg. Employing data from 6,975 contests, modelling reveals that what constitutes a good result has changed substantially over time. Generally, clubs which play at home in the first leg have become more likely to convert any given first-leg result to eventual success. Taking this trend into account, and controlling for team and country strength, a probit model is presented for use in generating probability estimates for which team will progress conditional on the first-leg scoreline. Illustrative results relate to ties where two average teams play each other and to ties where a relatively weak club plays home-first against a relatively strong club. Given that away goals serve as a tie-breaker should aggregate scores be equal after the two matches, the results also quantify how great the damage is when a home-first club concedes an away goal.