An amusement device seat assembly includes a seat to allow a passenger to sit. A leg space is provided under a seat base for holding a left and right leg of the passenger. The seat assembly includes a leg locking device for retaining an in the leg space introduced lower leg of the passenger. The leg locking device includes a central mount for preventing a laterally inwardly directed movement of a leg. A lateral mount prevents a forwardly directed movement of the lower leg. A bracket which may be operatable by the passenger himself is movable to provide an open or closed configuration of the leg locking device. In the closed configuration, an outer bracket extension prevents a laterally outwardly directed movement of a leg of a passenger. Advantageously, an intuitively working leg locking device is provided which contributes to a high level of operational reliability.