A week after it had been anticipated, one of the most looked-forward-to drills made its debut at Pittsburgh Steelers training camp. A “backs on backers” session was held during a rain-shortened session Monday at Saint Vincent. Monday’s drill did not seem to last as long as backs on backers did in the past, and it lacked the familiar intensity. • Monday’s practice was halted midway through when a storm approached. • Former Steelers teammates Joe Haden and James Harrison were guests on the field at practice.