Rapid weight loss or “weight cutting” is a dangerous practice that is ubiquitous in modern combat sports yet underrepresented in the medical literature. We present a case of exertional rhabdomyolysis in a mixed martial artist with sickle cell trait to illustrate the hazards of weight cutting and ensuing critical illness. Sickle cell trait is known to predispose patients to exertional rhabdomyolysis, and multiple fatal cases have been reported in the setting of strenuous exercise. Dehydration and consequent electrolyte abnormalities make combat sport athletes with sickle cell trait particularly vulnerable to this entity. This case suggests a potential role for sickle cell trait screening in this population and underscores the need for safer weight-control practices and monitoring among all combat sport athletes.