A sprain is the stretching or tearing of ligaments, which connect adjacent bones and provide stability to a joint. An ankle sprain is a common injury that occurs when you suddenly fall or twist the joint or when you land your foot in an awkward position after a jump. Most commonly it occurs when you participate in sports or when you jump or run on a surface that is irregular. Ankle sprains can cause pain, swelling, tenderness, bruising, stiffness, and inability to walk or bear weight on the ankle.