The current state-of-the-art sensory devices have enabled a reliable tracking of the human's movements. This had a positive impact on the medical field in general and on the physical rehabilitation domain in particular since it created new possibilities to the patients to train from their homes. Home-based rehabilitation systems have emerged as promising assistive tools for effective training and diagnosis. In order to provide a productive training experience, these systems should provide good assessment reports for both the patient and the clinician. The objective of this work is to form a metric to evaluate the ankle motion for rehabilitation applications. For this purpose, we use our sensory-mounted wobble board as an input interface to play a specially developed computer game that offers an intuitive and entertaining training experience. We invite 15 healthy subjects to test our system. The data collected during the play are used to derive a set of benchmarks for a number of parameters, namely the angular velocity and jerkiness.