Steve Cannon, the former head of Mercedes-Benz USA, is switching careers, becoming CEO of Atlanta-based AMB Group, a sports and business empire that includes the Atlanta Falcons football team. Cannon unexpectedly left Mercedes this week after four years as its U.S. president and chief executive officer. Initial reports had suggested that he had left due to weakening brand performance. The former West Pointer will handle strategy and management for the AMB Group following the official retirement of its founder Arthur M. Blank.