Days before their preseason opener, the Tennessee Titans found out the player they expected to be their starter at right guard, Saadiq Charles, had decided to retire at just 25 years old. Charles' decision creates a new opportunity for 2021 second-round pick Dillon Radunz, and adds to the questions that already exist about the offensive line overall, the right side in particular. ... More than two weeks into training camp, Tennessee finally signed veteran safety Quandre Diggs, a three-time Pro Bowler who did not miss a single game over the past four seasons with Seattle. Diggs does not have great size -- he is 5-foot-9, 197 pounds -- but he adds elements of speed and range that likely have been missing from the rear of the defensive backfield. ... Coach Brian Callahan said all starters who are healthy enough -- with the exceptions of defensive tackle Jeffery Simmons and outside linebacker Harold Landry -- should expect to play some against San Francisco. That will be a distinct departure from recent years under Mike Vrabel and should give an indication of how well players have picked up the new schemes installed by Callahan and his staff. ... As always, newcomers and players down the depth chart will be the ones to watch in the preseason. This year, that includes guys like rookie defensive lineman T'Vondre Sweat, who has to show he is as good as he has looked on the practice field, and third-year quarterback Malik Willis, who this time is fighting for a roster spot.