A Horrific Crash. A Mangled Leg. A Crazy Fast Comeback.

The American ski racer Nina O’Brien’s notorious crash and fractured leg shook the Olympic skiing competition. Nine months later, she is racing again.

For Nina O’Brien, Killington is the next step in a comeback that has stunned even the most optimistic of her coaches and doctors.Credit...Kimmo Brandt/EPA, via ShutterstockYou remember Nina O’Brien.

The American Alpine skier tore down the giant slalom course at the Beijing Olympics and crashed in a violent tumble two gates from the finish, leaving her lower left leg and foot twisted in the wrong direction, bone protruding from her skin.

Just nine months after the crash and two months after easing down the gentlest of hills for the first time,…