This study examined whether pre-existing situational motivation correlates with the magnitude of performance improvement elicited by verbal encouragement (VE) in long jump. A total of 134 physically active sports science students (21.1 ± 1.4 years) performed a long jump task under two conditions: with and without peer VE. Situational motivation, differentiated into autonomous (Intrinsic Motivation [IM], Identified Regulation [IR]) and controlled (External Regulation [ER], Amotivation [AM]) forms, was assessed immediately prior to trials using the Situational Motivation Scale (SIMS). Performance improvement was calculated as the percentage change (Δ%) between conditions. Paired t-tests evaluated the overall effect of VE, while multiple linear regression analysis was used to assess the predictive relationship between situational motivation subscales and performance gains (Δ%), with sex included as a covariate. The results showed that VE significantly enhanced performance across both sexes (p < 0.001; d = 1.109–1.331). The regression models indicated that Δ% was positively predicted by autonomous forms of motivation (IM: R² = 0.252; IR: R² = 0.262) and negatively predicted by controlled forms (ER: R² = 0.27; AM: R² = 0.249). Sex was not a significant predictor in any model (p > 0.05), indicating that all observed relationships were consistent across both male and female participants. These findings indicate that the performance-enhancing effect of VE in long jump is associated with the initial motivational state of the practitioners, being greater in autonomously motivated individuals and attenuated in those with controlled motivation. Consequently, situational motivation should be assessed before implementing VE in long jump, as its effectiveness is limited in individuals with low autonomous drive and may require preliminary strategies to enhance task engagement.