SI Now: Is mental fatigue a factor in the U.S. Open?

On Friday's SI Now, Sports Illustrated Senior Writer Alan Shipnuck discusses how fatigue plays a role in sports, and why the U.S. Open is the

On Friday's SI Now, Sports Illustrated Senior Writer Alan Shipnuck discusses how fatigue plays a role in sports, and why the U.S. Open is the most mentally challenging of the Majors.