Sickle cell trait (SCT) can pose a grave risk for some athletes. In the past decade in NCAA Division I football, no deaths have occurred from the play or practice of the game, but 16 deaths have occurred from conditioning for the game, and 10 (63%) of these deaths are tied to SCT, an excess of up to 21-fold. Research shows how and why, during intense exercise bouts, sickle cells can accumulate and "logjam" blood vessels, causing explosive rhabdomyolysis that can kill. Sickling can begin in 2 to 5 min of all-out exertion and can reach grave levels soon thereafter if the athlete struggles on or is urged on by coaches despite warning signs. Sickling collapse is an intensity syndrome that differs from other common causes of collapse. Tailored precautions can prevent sickling collapse and enable athletes with SCT to thrive. Irrationally intense conditioning for a game puts the lives of healthy athletes with SCT at risk.