A sprain is an injury to the stretching or tear of a tendon, the strong, fibrous tissue that connects the thumb bone. A sprain can be caused by abnormal flexion during a fall on an outstretched hand. Sprains are common in ball games (such as football, basketball, and handball) and games involving a stick or racket (such as hockey). A thumb sprain involving the collateral ligament may be referred to as skier's. ( gamekeeper's) thumb