A sprain is an injury to the ligaments around a joint. Ligaments are the strong, flexible fibers that connect one bone to another. When a ligament is stretched too far or tears, the joint will become painful and swell. An ankle sprain can range from mild to severe depending on how badly the ligament is damaged. Most ankle sprains happen when you make a rapid shifting movement with your foot planted, like when playing soccer or being tackled in football. A sprain can occur in an event as simple as accidentally rolling your ankle.