Prior research showed that swimmers swim faster in relay than in individual competitions if they start at later relay positions. This finding is typically explained via the swimmers’ relay position and their associated perception that their individual performance is indispensable for their teams’ performance. Using multilevel modeling, the authors disentangled this situational explanation from alternative accounts focusing on individual differences between swimmers. Two studies empirically supported the situational explanation: When using a within-person approach and, thus, controlling for between-person variance (i.e., individual differences between swimmers), the swimmers’ relay position remained a significant predictor of the increases in effort spent in relays. This finding held when controlling for the on-average higher instrumentality in the relay versus the individual competitions. Thus, the often observed effort gains in swimming relays probably are due to the swimmers’ relay position as a situational explanation and stem from the motivating impact of teamwork versus individual work.