A muscle cramp is a strong, painful contraction or tightening of a muscle that occurs suddenly and mostly in the legs (hamstring and calf muscles). These spasms may last from a from a few seconds to several minutes. Any person of any age can get these muscle cramps, but the occurrences are high for athletes, sportspersons, and runners.
This may be due to an exhausting physical activity which results in loss of sodium content and electrolytes from the body, which results in electrical misfiring. One more explanation of why these cramps occur in athletes and sports persons is, muscles tend to cramp specifically when they are overworked and fatigued. The tiredness of the muscles increases muscle cramps.