What key variables differentiating positions across age categories in rugby union?

Potential estimation (PE) in rugby union traditionally emphasizes physical, anthropometric, and biological attributes to distinguish between playing positions. Forwards are typically characterized by greater strength and power, whereas backs rely more on speed and agility. However, how these differentiators evolve across developmental stages remains underexplored. This study aimed to examine age-related changes in discriminative variables influencing positional differentiation across U14, U16, and U18 categories. A total of 139 national level male rugby players were assessed: U14 (n = 64), U16 (n = 51), and U18 (n = 24). Anthropometric data (height, body mass, body mass index (BMI)), maturity status (Y-PHV, MO), sprint performance (T10, T30), and horizontal force-velocity (F- v ) profiling were collected. ANOVAs and post hoc analyses explored differences across age and position. Decision tree models identified key discriminative variables, and a feature importance analysis was performed, complemented by a recurrence analysis. Findings revealed significant age- and position-related differences (p < 0.05). BMI and maturity variables were the most relevant at U14, while sprint and F- v metrics gained importance with age. In U18, physical performance indicators such as peak power, theoretical maximal horizontal force, and slope force velocity emerged as dominant. These results suggest a transition from anthropometric to performance-based differentiation across age groups, offering key insights for refining PE strategies in youth rugby.