Contact Role and Tackle Characteristics Shape Head Acceleration Exposure in Male Community Rugby: A Cohort Study Utilising Instrumented Mouthguards

Background: Rugby Union has attracted increased scrutiny due to concerns over head acceleration events (HAEs), particularly regarding their frequency, severity, and potential long-term health implications. While substantial efforts by governing bodies have focused on reducing head impact risks through education, regulatory changes, and the introduction of instrumented mouthguards (iMGs), limited data exist for the community rugby context, especially across different age grades and playing positions. Objective: To quantify HAE across playing positions, age grades, and contact phases in community rugby, and to identify match scenarios associated with high-magnitude head loading. Methods: A prospective observational cohort study included 259 male players across U13, U15, U19, and Premier senior men’s grades. Players were fitted with iMGs, and match play was video recorded for verification. HAEs were identified from iMG-triggered acceleration events (SAEs) >5g and coded for match context, player position, and contact event characteristics. Statistical models evaluated differences in HAE frequency, incidence rates, and head kinematics (Peak Linear Acceleration [PLA], Peak Angular Acceleration [PAA], Rotational Velocity Change Index [RVCI]) across grades, positions, and contact scenarios. Results: A total of 7358 HAEs were verified from 8593 SAEs across 72 matches. Tackles and rucks accounted for ~60% of all HAEs. High tackles significantly increased head loading in ball carriers (PLA: +4.16 g, p = 0.02; PAA: +443 rad/s², p = 0.002; RVCI: +1.87 rad/s, p = 0.04), while low tackles elevated head loading in tacklers (PLA: +4.9 g, p = 0.004). Upright tacklers were more likely to produce high tackles (p < 0.001) and head-to-head contacts (p = 0.019). U13 ball carriers showed higher rotational loading than tacklers (RVCI: +5.01 rad/s, p = 0.008), likely reflecting frequent secondary mechanisms such as head-to-ground and body-to-ground. Defensive rucks carried greater HAE risk than attacking rucks (all p < 0.05), particularly for U19 jacklers (IRR = 2.27, p < 0.0001). Conclusions: Tackles and rucks are primary sources of HAEs, with risk shaped by posture, tackle height, and player role. Lower tackle heights reduce ball carrier load but increase tackler exposure, indicating a potential safety trade-off. Younger players, particularly U13s, were more susceptible to secondary impacts (e.g., head-to-ground), potentially due to limited task-specific experience and underdeveloped control during the tackled phase. Position- and age-specific strategies may be required to optimise safety and reduce HAE risk across all levels of community rugby.