The study investigated effects of in-season head-coach changes (HCC) on the subsequent team performance in men's English, German, and Spanish premier soccer leagues. A pre-post matched-controls design involved 149 HCC-teams and 3,960 games in 2010-19. Analyses (paired t-test, repeated-measurement ANOVA) revealed five central findings. 1. An HCC was preceded by a spell of under-performance, with a particular performance collapse in the two last pre-HCC rounds. 2. Performance showed an instant, strong improvement in the first post-HCC game. 3. The performance remained increased up to 16 post-HCC rounds. 4. Post-HCC performance also exceeded teams' initial baseline performance earlier before the HCC. Accordingly, the summed performance through 8, 12, and 16 post-HCC rounds exceeded the performance through 8, 12, and 16 pre-HCC rounds (0.92 < Cohen's d < 1.17). 5. HCC-teams' pre-post performance development differed from matched non-HCC control teams. In sum, the present evidence suggests positive short, medium, and long-term HCC effects at the highest professional soccer level. Theoretical hypotheses discussed in the literature - the "common-sense," "ritual-scapegoating," "vicious-circle," and "mean-reversion" hypotheses - are partly inconsistent with the present evidence. However, the evidence is fully consistent with a new hypothesis introduced here: the hypothesis of relief from a coach's performance-suppressing factor (RCPSF).
Keywords: Professional soccer; coach dismissal; international; performance; theory.