Biomechanics of rugby tackling in amateur youth players

Tackling is a fundamental component of rugby union and rugby league, with consequences for both performance and player safety. In youth rugby, the tackle is the leading cause of concussions, and common technical errors, such as head-in-front positioning, may be modifiable through coaching. Despite this, a clear account of safe tackling mechanics in youth remains limited. This thesis investigates tackle ability and kinematic characteristics in youth rugby and translates those findings into coachable insights. First, an introduction to what is currently known about tackle-related injury risk and technique, the methodological challenges of quantifying collision biomechanics, and how markerless motion capture can be used to study youth tackle kinematics. Second, a systematic review compares adolescents with adults to identify age-related differences in head placement, trunk and lower-limb flexion, shoulder-led contact, arm wrap, and associated head-loading risk. Third, an experimental study using Theia3D quantifies adolescent kinematics under controlled conditions across four coached executions defined by target height (regular or low) and shoulder side (dominant or non-dominant). Finally, evidence from both studies is synthesised to answer two questions: 1) how do tackle kinematics vary by age from adolescents to adults, and 2) what characterises the biomechanical execution of a safe tackle in adolescents, and what are the coaching implications for improving safety. The systematic review found that youth players often demonstrate head-in-front positioning, whereas adults show deeper hip and knee flexion and a more stable, lower-limb driven tackle shape. The experimental study found that target height was the primary determinant of tackle execution at contact; low targets increased trunk and neck flexion, and centre-of-mass velocity did not differ across conditions, indicating that these postural changes were not explained by approach speed. Overall, this progression from synthesis to experiment provides an objective, biomechanical foundation for adolescent coaching and identifies clear priorities for future work linking technique changes to head-loading and injury outcomes.