Nearly six months later, the images of Alabama running back Najee Harris in college football’s national-championship game remain vivid: bursting into the open, bouncing off tacklers, making a loud splash on the sport’s biggest stage. Now he’s eager for an encore. Harris, the country’s No. 1 recruit in the class of 2017 at Antioch High School, peers toward the start of training camp early next month with a curious mix of bravado and skepticism. His six-carry, 64-yard performance in the title game might have showed the world his readiness, but he already brimmed with quiet confidence. That’s why he contemplated leaving Alabama after his freshman season, frustrated by sparse playing time.