A common injury caused by a twisting over on the ankle (the ankle usually rolls outward as the foot turns inward) resulting in overstretching or tear in one of more ankle ligaments. 

 

An ankle sprain usually causes immediate pain, swelling, brusing and tenderness near the site or the ligament, and ranges from mild to severe. The degree of pain and swelling is usually an indicator of the severity of the injury.  

 

In a severe sprain the ankle ligaments may have completely torn and the person is usually unable to bear any weight on the ankle due to severe pain and a feeling of instablity

 

This injury is common in sports such as football, but can occur when walking on an uneven surface eg. over fields, or raised paving stones or simply stepping down a step.  .