The Denver Broncos’ running-back depth took a hit during their first intersquad scrimmage at Sports Authority Field on Saturday. Mario Fannin suffered a torn Achillies tendon, ending his season. Fannin tore his ACL in training camp last year and missed all of 2011, but had a chance to make the practice squad this season before his latest injury. The Broncos did add to their depth in the secondary with a free-agent signing over the weekend. Eight-year veteran safety Jim Leonhard agreed to a deal with the Broncos. He’ll be placed on the Physically Unable to Perform list while he completes his rehab from a torn ACL that cost him the end of the 2011 season, but once healthy, Leonhard provides a veteran presence in a youthful safety corps. The former Bill, Raven and Jet could also have an opportunity to return punts for the Broncos.