The least athletic American president is Calvin Coolidge, whose athletic talent can be encapsulated by the way he played and felt about golf.
Golf's popularity took off during the first quarter of the twentieth century. As such, presidents were expected to play and enjoy the game. Well, Coolidge played, but he didn't enjoy. By all accounts, he would have been jealous of Charles Barkley's golf swing, routinely taking 10+ strokes to get to the green. And when it came time to leave the White House to make way for Herbert Hoover, the only item left behind was his bag of golf clubs.
Coolidge's disdain for sports didn't end at his own poor abilities. Sports, in a way, also killed his son. In 1924, Calvin Jr. developed a staph infection after playing tennis barefoot on the White House courts. The infection went untreated for too long and soon killed him.