Walston (elbow) threw live batting practice Friday, Jesse Friedman of GoPHNX.com reports.
Walston touched 94 mph during the session, an encouraging sign considering he hovered between 91 and 92 mph during his three appearances this season. The 23-year-old southpaw is expected to be activated from the injured list sometime in August, but manager Torey Lovullo indicated Friday that the team was still determining whether he'll be an option for the big-league rotation down the stretch.