Of these hazards, brain injuries were well known to be of serious concern. In 1929, Eddie O’Brien, a doctor and football official, urged that administrators require a physician to attend all school football matches, citing examples of players knocked unconscious or “out on their feet” who were allowed to remain in the game. He used the term punch-drunk to describe “the condition caused by head injuries and lack of medical attention.” The phrase, which referred to the state of confusion resulting from many hits to the head, was mostly associated with boxing. But physicians clearly understood that repeated blows in football could also cause significant cognitive harm.

Given the risks, a 1938 Journal of School Health article advised against football for boys under 16 years of age, noting that “more concussions occur in football than is generally realized.” That same year, Augustus Thorndike, a physician who played a key role in the development of sports medicine, complained that most laypeople were unaware of the serious complications that might result from “a simple concussion of the brain.” In the decades to follow, many other medical experts would express similar frustration with Americans’ willingness to disregard the brain’s vulnerability to repeated impacts. In 1951, the neurologist Frederic Gibbs lamented that children were “encouraged to addle their own brains with repeated concussions in such sports as football and boxing.” Writing in the American Journal of Public Health, Gibbs urged that the next generation be taught instead to appreciate the importance of the brain.

To that end, in a 1952 New England Journal of Medicine article, Thorndike recommended limits on how many brain injuries athletes might sustain in their careers.