I have a few quick rules of thumb:
1- A large amount of swelling
2- Bruising extending beyond the outside of the ankle
3- Inability to walk on the foot/ankle
4-Pain that doesn't resolve after a few days of rest and icing. 
5-If you need to return to running or sports quickly any ankle injury should be seen as soon as possible. 
Dr. Misty McNeill
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D.P.M. - Founder of Prairie Path Foot and Ankle Clinic