By the time Roosevelt entered the White House in 1901, however, the gridiron had turned into the sports version of a killing field — largely because of the harsh protocols of early football. The forward pass was forbidden, for instance, and teams were encouraged to advance through mass formations of sheer brutality. “We’re coached to pick out the most dangerous man on the opposing side and put him out in the first five minutes of the game,” one Princeton player explained to the journalist Henry Beach Needham in 1905. The Chicago Tribune reported that 19 people died playing college, high school and sandlot football that year.

T.R. was increasingly unsettled by muckraking reporting of the sport’s deadly excesses — which foreshadowed today’s alarms about the long-term dangers of football concussions — but he was also determined to stop what he called the “baby act” of Harvard’s president, Charles William Eliot, and other college officials, who were trying to abolish the game altogether.

What may have had a more profound effect on Roosevelt, dramatizing the genuine dangers of the sport, was the early football playing of his eldest son, Theodore Roosevelt Jr., whom the family called Ted. American history abounds with politicians who are mobilized to address controversial issues when a family member is involved, and T.R. was very close to his children.

When young Ted injured his front teeth and collarbone playing football at Groton School in Massachusetts in 1902, President Roosevelt wrote the headmaster, the Rev. Endicott Peabody, that “Ted would have a fit if he knew I were writing” but that “if he goes on like this he will get battered out before he can play in college.”

The president warned his son by mail that in football, “the very things that make it a good game make it a rough game.” He wrote Ted that “the chance of your damaging yourself in body is outweighed by the possibility of bitterness of spirit if you don’t play,” so he would allow him to continue the sport. But he jocularly insisted, “Now do not break your neck unless you esteem it really necessary.”