4 | 99 The transition to adulthood: A game changer!? ABSTRACT This study investigates the relationship between major life events and sport participation during the transition to adulthood. Two waves (2009 and 2013) of a Dutch panel study provided information on education, employment, relationship, civil/marital status, and parenthood for 2829 Dutch citizens (ages 15–45) and their sport behaviour. Our analyses indicate that respondents who left full-time education, began to work, entered and/or formalised a relationship, and became a parent participated less frequently in sport than those who did not (between-person differences). Moreover, experiencing these events reduced sport frequency (within-person changes). All events except beginning to work reduced the number of sports practised. However, additional analyses of the interaction effects between major life events and gender indicate that the between-effects of work on the number of sports and sport frequency are negative for men, but positive for women. Further, those who entered an intimate relationship were more likely to switch from a “heavy” club-sport setting to a “lighter”, more individualised setting and to stop practising sport altogether, compared to those who stayed single. Those who left full-time education and started working were more likely to continue sport in a club setting, compared to those who continued education and did not start working. Sport providers, programmes, and policies could use these results to inform efforts to pre-empt impacts of major life events, thus curbing drop out and retaining sport participants, especially during the transition to adulthood. Keywords: life events; sport participation; sport club membership; adulthood; transitions. A slightly different version of this chapter has been published in the European Journal for Sport and Society (Van Houten et al., 2019). Co-authors are Prof. Dr. G. Kraaykamp, and Asst. Prof. Dr. B. Pelzer. Previous drafts of this chapter have been presented in August 2017 at the European Sociological Association conference in Athens (Greece), and in November 2017 at the “Dag van het Sportonderzoek” in Zwolle (the Netherlands).