The most frequent causes of fractures are falls and motor vehicle crashes. There is a higher incidence of fractures in some sports that involve prolonged impact, high impact, balance, or high speeds. Stress fractures can result from prolonged impact or repetitive forces. For example, running or jogging can cause stress fractures in the leg, foot, ankle, or hip. High impacts can occur during contact sports, including tackles in football or punches in boxing. Skateboarding, bicycle riding, and snow skiing are sports that involve balance and speed. Fractures can occur during contact with a hard surface, for instance during a fall to the cement while skateboarding or during contact with an object, such as a tree while snow skiing.