Background <p>Soccer requires frequent high-intensity decelerations, braking actions, and multidirectional re-accelerations. Flywheel resistance training may provide a braking-oriented inertial stimulus that is relevant to change-of-direction (COD) performance. However, randomised controlled evidence directly comparing unilateral flywheel resistance training with unilateral traditional resistance training in high-level soccer players remains limited. This study compared the effects of unilateral flywheel resistance training and unilateral traditional resistance training on COD-related performance in high-level male soccer players.</p> Methods <p>Twenty-six high-level male soccer players were randomly allocated to a flywheel resistance training group (FRT, <i>n</i> = 13) or a traditional resistance training group (TRT, <i>n</i> = 13), and 22 players completed the study and were included in the final analysis (FRT, <i>n</i> = 11; TRT, <i>n</i> = 11). Both groups completed an 8-week intervention twice per week in addition to regular soccer training. The unilateral Bulgarian split squat was used in both groups, with training structure and movement pattern matched between conditions. Performance was assessed before and after the intervention using 10-m and 30-m linear sprint tests, the T-test, Pro-agility test, Arrowhead change-of-direction test, and AFL-derived change-of-direction tasks performed without and with the ball. Intervention effects were analysed using Bayesian repeated-measures analysis of variance, with evidence for the group × time interaction quantified using inclusion Bayes factors (BFincl).</p> Results <p>The FRT group showed greater improvements than the TRT group in the T-test (BFincl = 135.96), Pro-agility test (BFincl = 107.01), Arrowhead-L (BFincl = 34.55), Arrowhead-R (BFincl = 25.63), and AFL-derived COD task without the ball (BFincl = 17.33). Evidence for an interaction was moderate for the AFL-derived COD task with the ball (BFincl = 3.24), anecdotal for the 10-m sprint (BFincl = 2.52), and favoured no interaction for the 30-m sprint (BFincl = 0.64).</p> Conclusions <p>Under matched unilateral movement conditions, flywheel resistance training was associated with greater reductions in completion time than traditional resistance training across several pre-planned COD tasks in high-level male soccer players. However, this pattern was less consistent for linear sprinting and the ball-constrained AFL-derived COD task, suggesting task-specific transfer of training adaptation.</p> Trial registration <p>ClinicalTrials.gov, NCT07567677. Retrospectively registered on 28 April 2026.</p>