One of the most common sporting injuries is a sprain to the ligaments on the outside of the ankle. This occurs when the ankle 'rolls' outwards and the ligaments are overstretched. This is often caused by weakness in the ankle when it is put in a more challenging situation, for example, stepping in a hole or off a curb.
It is best to see a physiotherapist ASAP after injury to assess the damage, get appropriate treatment and rehabilitation to get the best recovery
Reference: Hubbard, T.J., Wikstrom, E.A., 2010, Ankle sprain: pathophysiology, predisposing factors, and management strategies, Open Access J Sports Med., 1: 115–122.