This study identified helpful and unhelpful encouragement at mass participation running events and explored the meaning that runners found in encouragement. First, 10 k and half-marathon postevent surveys differentiated instructional and motivational components of helpful and unhelpful support. Second, an inductive, reflexive thematic analysis of 14 interviews highlighted the reciprocal relationship between the crowd and runners, whereby quality of support was reflected in runners’ emotions and behavior. Participants drew pride in participation and belief from the crowd, and they wanted to “give back” through doing their best. Personal and authentic support was particularly valued. Although support was widely appreciated, at times it created a pressure to “perform.” As a novel intervention based on our combined findings, we recommend that crowds, event organizers, and psyching teams give encouragement “with IMPACT” (Instructional; Motivational; Personalized; Authentic; Confidence-building; Tailored to the distance). Crowds should also demonstrate the “core conditions” of authenticity, empathy, and being nonjudgmental within their encouragement.