Today, C.T.E. is the subject of furious controversy. Some of the debate has been stoked by researchers affiliated with the sports industry, who argue that we still don’t know for sure that head blows in football, hockey, soccer, or rugby can lead, decades later, to the dramatic mood problems, the personality changes, and the cognitive deterioration associated with C.T.E. These experts maintain that, before we rethink our relationship with these sports, we need scientific inquiries that meet highly rigorous standards—including longitudinal studies that would take fifty to seventy years or more to complete. In the meantime, millions of children and high-school, college, and pro athletes would continue butting heads on the field.
Casper believes that the science was convincing enough long ago. “The scientific literature has been pointing basically in the same direction since the eighteen-nineties,” he told me. “Every generation has been doing more or less the same kind of studies, and every generation has been finding more or less the same kinds of effects.” His work suggests that, even as scientific inquiry continues, we know enough to intervene now, and have known it for decades. It also raises important questions about how, and how much, old knowledge should matter to us in the present. If Casper is right, then how did we forget what’s long been known? And when does scientific knowledge, however incomplete, compel us to change?
According to Casper and other historians, the collision between sports and concussions began around the eighteen-eighties. American-style football, a descendant of rugby, was gaining in popularity at Ivy League colleges, and violence was fundamental to its allure. Players who wore stocking caps but no padding executed mass plays, such as the “flying wedge,” that led to savage clashes. Sometimes, young men died on the field. “Concern about concussions has a history in football as long as the game of football itself,” Emily Harrison, a historian who teaches epidemiology and global health at the Harvard School of Public Health, told me.
Football’s “first concussion crisis”—which Harrison wrote about in 2014—ensued after a study of Harvard’s football squad in 1906 reported a hundred and forty-five injuries in one season, nineteen of them concussions. In a commentary, the editors of the Journal of the American Medical Association (JAMA) singled out cases in which “a man thus hurt continued automatically to go through the motions of playing until his mates noticed that he was mentally irresponsible.” This behavior, they noted, suggested “a very severe shaking up” of the central nervous system, which, they argued, might have serious consequences later in life. Football, they concluded, was “something that must be greatly modified or abandoned if we are to be considered a civilized people.”