David Ortiz stepped into the box yesterday and began spraying soft line drives around one of the batting practice fields at JetBlue Park. With each successive round, however, those soft liners stiffened. They started one-hopping the fence, and eventually turned majestic. One of his last swings dented the corrugated steel structure beyond the right field fence. The Red Sox can only hope the performance serves as a metaphor for his season. It has taken Ortiz some time to ramp up this spring, and even now the uncertainty in his voice is apparent when he discusses the Achilles injury that just won’t go away. Diagnosed as a slight tear last season, it has since healed, but not before leaving an area of calcification behind the tendon that causes irritation every time it snaps back and forth, which, when you’re a professional athlete, is a lot. “Every time you bend that tendon you feel it, and I’m a big boy, you know what I’m saying?” Ortiz said yesterday. “It puts more stress.” Ortiz ran the bases for the second time this spring, and much like his BP session, required a few reps to get going. He sprinted gingerly to first base three times before opening it up and rounding the bag twice on faux singles.