Shared leadership is described as the dynamic process of distributing leadership influence across multiple team members. It is viewed as an effective form of management to deal with increased complexity in youth team sport. However, literature on youth leadership development and reliable and valid measures to assess shared leadership in youth sport is still lacking. This paper seeks to make a contribution to the youth leadership literature by developing an instrument to measure shared leadership among young football players. A total of 746 U17 players from 62 different youth football teams in two samples in The Netherlands were surveyed. The Youth Athlete Shared Leadership (YASL) in football instrument comprises three factors: ‘steering’, ‘coaching’ and ‘intervening’. This research contributes to the common understanding of youth leadership development in general and youth team leadership in particular. The practical contribution is a tool for coaches to develop shared leadership behavior in youth football.