A stress fracture is a fatigue-induced bone fracture caused by repeated stress over time. Instead of resulting from a single severe impact, stress fractures are the result of accumulated injury from repeated submaximal loading, such as running or jumping. Because of this mechanism, stress fractures are common overuse injuries in athletes.

Stress fractures can be described as small cracks in the bone, or hairline fractures. Stress fractures of the foot are sometimes called "march fractures" because of the injury's prevalence among heavily marching soldiers. Stress fractures most frequently occur in weight-bearing bones of the lower extremities, such as the tibia and fibula (bones of the lower leg), metatarsal and navicular bones (bones of the foot). Less common are stress fractures to the femur, pelvis, and sacrum. Treatment usually consists of rest followed by a gradual return to exercise over a period of months.