One night in early April, 1958, Joyce Glassman’s doorbell rang and woke her. An aspiring novelist who worked as a secretary at a small publishing firm, Glassman lived in a tenement on East Thirteenth Street, in Manhattan. When she opened the door, she found Jack Kerouac, his face covered in blood. The two had met the year before, on a blind date arranged by Allen Ginsberg. In her memoir “Minor Characters,” Glassman recalls Kerouac staggering inside, supported by the poet Gregory Corso. “Leave me alone,” Kerouac moaned, as Glassman tried to wipe the blood from his face. He looked stunned.

In Glassman’s telling, Kerouac and Corso had been barhopping in Greenwich Village. At Kettle of Fish, on MacDougal Street, a stranger accused Kerouac of insulting him. When Kerouac and Corso left the bar, the stranger and his friends surrounded them, and the man threw Kerouac to the ground and beat his head against the curb. (There are other versions of the story, but Kerouac’s correspondence suggests that Glassman is mostly correct.)

Over Kerouac’s protests, Glassman writes, she brought him to a nearby hospital. She was worried that he had a concussion. But, according to the doctors, Kerouac had suffered only cuts and bruises. He was given some medicine and a bandage on his forehead.

Within days, Kerouac began to suspect that he had been misdiagnosed. Less than a year later, in a letter to Ginsberg, Corso, and Peter Orlovsky that was later published by biographer Ann Charters, in one of her collections of his correspondence, he noted his “recent belligerent drunkenness,” and said, “I just noticed today it all began last April right after that bum pounded my brain … maybe I got brain damage, maybe once I was kind drunk, but now am brain-clogged drunk with the kindness valve clogged by injury.”

Glassman, who has since taken the last name of her late husband, the abstract painter James Johnson, recently came to think that this incident might be more significant than she had previously imagined. While researching a biography of Kerouac several years ago, she became aware of reports of men whose lives had followed a trajectory like Kerouac’s after the beating: a relentless decline marked by substance abuse, depression, and memory loss. Like Kerouac, who died at forty-seven in 1969, of an internal hemorrhage possibly brought on by alcoholism, many of these men had reached the pinnacle of their field only to implode in middle age. Like them, Johnson saw, Kerouac had suffered head trauma—and not once, but many times, for, in addition to a serious car accident in his teens, he’d spent years participating in the same activity that had landed most of them in the headlines: football.

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Kerouac played his first down in the fall of 1935. He was thirteen. The game took place in a sandlot in Dracut, a suburb of Lowell, Massachusetts, his home town. There were no helmets, no referees, just two bands of scruffy kids tackling each other; a pair of men used a homemade chain to measure first downs. One end zone was marked by a pine tree, the other by a peg. Kerouac crossed the goal line, such as it was, nine times.

That, at least, is the account Kerouac gives in “Vanity of Duluoz,” an autobiographical novel. Just as “On the Road” fictionalizes his adventures with Neal Cassady, the book dramatizes the years in which he traversed the gridiron. Along with “The Town and the City,” his first novel, it stands as his only major writing about his football career, which lasted seven years and carried him from Lowell High School to Columbia University.

At times, the books make for a harrowing read. The worst moment occurs in an early chapter of “Vanity of Duluoz.” Playing for Horace Mann, the prep school he attended for a year before matriculating at Columbia, Kerouac takes off on a long run. About to score, he feels a pull at the back of his neck—one of his opponents grabbing him by the shoulder pads and yanking him to the muddy turf. He loses consciousness. Once he wakes up, his coaches deem him fit to return to the game. Standing in the huddle, he asks himself, “What are we doing on this rainy field that tilts over in the earth, the earth is crooked, where am I? Who am I? What’s all that?”

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Earlier this year, I ventured into the Henry W. and Albert A. Berg Collection of English and American Literature, in the New York Public Library, which houses the bulk of Kerouac’s archive. I wanted to see if I could answer a question Johnson poses in her recent biography, “The Voice Is All: The Lonely Victory of Jack Kerouac”: “Did the effects of cumulative damage to the brain over Jack’s lifetime … contribute to his deepening alcoholism and depression?”

If it were possible to examine Kerouac’s brain, the question could, perhaps, be answered definitively. We could learn, for instance, if he suffered from chronic traumatic encephalopathy, the progressive neurodegenerative disease that has been found, so far, in the brains of more than fifty former football players. Because C.T.E.’s symptoms overlap with those of Alzheimer’s disease and other forms of dementia, it can be diagnosed only by autopsy, and Kerouac didn’t leave his brain to science.

Still, he did leave his writing, which, along with the recollections of his friends and acquaintances, provides a certain amount of insight into his medical history. I assembled what I found about Kerouac’s head injuries and decline into a dossier and sent it to a handful of experts on the subject.

“Kerouac had all of the symptoms of C.T.E.,” Robert Cantu, a neurosurgeon and co-director of Boston University’s Center for the Study of Traumatic Encephalopathy, told me. “I don’t think it’s possible, especially since you cannot be certain about the presence of C.T.E. without examining somebody’s brain, to other than speculate about whether he may have had some of his issues as a result of brain trauma. My gut feeling is he did.”

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Although Kerouac is known as the father of the Beat Generation, his youthful diaries treat nothing so passionately as sports. His first entry in 1938 notes the results of the Rose and Cotton Bowls, and offers predictions for the Santa Anita Derby, the Stanley Cup, and the World Series, among other contests.

Kerouac paid even more attention to his own participation in athletics. The winter months of his 1938 diary assiduously report his performance as a member of Lowell’s varsity track-and-field squad. The summer months are filled with entries about baseball. Autumn brings dispatches from the football field, where he played running back. On Thanksgiving Day, 1938, Kerouac gleefully describes his role in defeating his school’s rival, Lawrence High: he caught a short pass and plowed into the end zone, scoring the game’s only touchdown.

The same diary records roughly fifty practices and ten games. Although he rarely left the bench in 1937, and probably never did in 1936, if he practiced regularly, he may have trotted onto the field more than a hundred and fifty times before leaving high school. Practices frequently included full-contact scrimmages.

The summer after high school found Kerouac in a celebratory mood. Frank Leahy and Lou Little, the head coaches of Boston College and Columbia University, respectively, had seen the touchdown he’d scored against Lawrence, and both had offered him a scholarship. But his happiness was marred by another head injury. On a road trip to Vermont, Kerouac and a friend were involved in a car accident, and he was hospitalized. Years later, in his journal, Kerouac would wonder if his mother had been right to ask if the accident had had a permanent effect on his head.