If girls and young women ruptured their A.C.L.’s at just twice the rate of boys and young men, it would be notable. Three times the rate would be astounding. But some researchers believe that in sports that both sexes play, and with similar rules — soccer, basketball, volleyball — female athletes rupture their A.C.L.’s at rates as high as five times that of males.

— "The Uneven Playing Field," a New York Times Magazine investigation of sports injuries. What's scary is that no one can figure out why A.C.L.s snap.