This descriptive laboratory crossover trial study examined the intervention of high friction synthetic vs lower friction natural sport surfaces on the ankle joint biomechanics in a sidestep cutting task. Twenty-nine male futsal players performed 5 trials of sidestep cutting task in a laboratory, recorded by an 18-camera motion capture system to obtain the ankle joint orientation, velocity and moment. Utilised friction was obtained by the peak ratio of the horizontal to vertical ground reaction force during the stance. Repeated measures (MANOVA) suggested a significant effect of the playing surface and post hoc paired t-tests revealed significantly higher utilised coefficient of friction, higher peak plantarflexion angle, lower peak eversion angle, higher peak inversion velocity, lower peak inversion moment and higher peak internal rotation moment. In performing a sidestep cutting task, futsal players demonstrated higher utilised ground friction when available friction from the playing surface was higher, resulting in higher peak inversion velocity and higher peak internal rotation moment, which may make the ankle joint more prone to sprain injury. Floorings for futsal should have an adequate coefficient of friction for agility and avoidance of the risk of slipping. Increasing the coefficient of friction may not only enhance performance but also endanger the ankle joint. [ABSTRACT FROM AUTHOR]