OBJECTIVES: To evaluate performance on selected reach directions of the Start Excursion Balance Test (SEBT) in an elite underage rugby union population, and determine if differences exist between the forward and back position units. This information may have implications for the application of this test in player injury prevention and management. DESIGN: Descriptive study. SETTING: Gymnasium at an elite junior rugby union screening camp. PARTICIPANTS: 102 healthy male elite rugby union players (age = 17.9 ± 1.1 years, height = 1.83 ± 0.07 m, body mass = 90.5 ± 11.3 kg). MAIN OUTCOME MEASURES: Participants were assessed on the Anterior (A), Posterior-medial (PM), and Posterior-lateral (PL) reach directions of the SEBT. RESULTS: Normative data for SEBT performance in the A, PM and PL reach directions were established for an elite junior rugby union population. No significant differences in dynamic postural stability were observed between the forward and back position units. CONCLUSIONS: This study provides normative SEBT data on an elite junior rugby union population, which enables clinicians to compare player dynamic postural stability and has implications for use in the prevention and management of player injuries.