Timing and tactical analysis of player substitutions in the UEFA Champions League

The aim of this study was to examine the influence of situational variables on timing and tactics of substitutions in elite soccer. The sample was constituted by 677 substitutions made over the 124 matches played in the 2013-14 UEFA Champions League. To determine factors that affect substitution times, one-way ANOVA and Student's t-test were used. In a second instance, a chi-square analysis was carried out to establish if there was an association between each situational variable and the tactics of substitution. Data mining technique (J48 decision tree) was used to find optimal splits in substitution times, which lead to enhanced probability of success. Coaches tend to hold onto substitutions later when the team is ahead, but make substitutions earlier when either tied or behind (P<0.001). The probability that the substitution would be offensive in tactical terms increases when a team is behind in a match (P<0.001). Coaches avoiding defensive substitutions when they face a worse-ranked team and showing an increased preference for them when they face a similar-ranked opponent (P<0.05). Finally, it can be suggested that coaches should be aware that reverting losing scenarios apparently requires to change tactics early in the match.