RED-S happens when the athlete eats too few calories, compared to what is being burned in practice and play, creating a state of malnourishment. RED-S is short for relative energy deficiency in sports. It used to be called female athletic triad, as it is most commonly observed in female athletes. Although it remains prevalent in women, it is seen occasionally in male athletes, too. That’s one reason for the name change. The other was to more clearly communicate its cause.