Bobby Crosby's back injury has sidelined him once again. The Athletics on Friday placed the shortstop on the 15-day disabled list, retroactive to Tuesday, with a lower back strain. This is the second stint on the disabled list for Crosby, who was sidelined from July 31-August 17 with the same injury. The 26-year-old also was shelved for 11 contests earlier this season due to triceps, hand and back ailments. He has missed 95 games over the last two seasons with injuries.