Can anyone tell me what causes a person to have leg cramps while running?

Muscle cramp: That could be 2/2 electrolyte imbalance, dehydration, overuse of muscle, injury to muscle, some medications like statin, depression med and birth control pills, low blood supply to the legs, please see your provider for evlauation. stay hydrated while running.

Lack of hydration.: Sometimes it's a lack of hydration or an electrolyte imbalance. Drinks such as Gatorade can help replenish what your body needs. Water intake is also important.