Ryan Zimmerman (thumb) took part in a full batting practice session and fielded infield ground balls on Wednesday. "Today," Nationals manager Matt Williams said, "was a big day for him." Zimmerman had been relegated fielding fly balls in the field, and he was only cleared to begin swinging and throwing on Monday. It's still unclear where he'll play upon returning -- he's been taking reps at first base and in left field while unable to field ground balls -- but all three positions, including his native third base, appear to be in play. The next step is a rehab assignment, which could come as early as the weekend.