Previous research has revealed a motivational effect of professional sports on amateur sport participation. However, research that attempted to analyze whether this motivational effect indeed transfers into observable behavior is scarce and inconsistent. Therefore, this paper intends to analyze whether the individually perceived relevance of professional sports causally increases the frequency of amateur sport participation. To test this hypothesis, an instrumental variable approach is employed using primary data of N=863 German amateur triathletes. The estimated models provide evidence for a causal effect: according to the 2SLS results, amateurs who perceive professional triathlons as being very important participated significantly more minutes per week in amateur triathlons.