The stars will be coming out for Saturday's Showtime Championship Boxing card in Phoenix.  Among those expected to attend the show are film star Russell Crowe, former undisputed heavyweight champion Mike Tyson and legendary rock star David Bowie. In a candidate for Fight Of The Year fight, Kostya Tszyu defends his junior welterweight world championship against IBF Interim 140-pound champion Sharmba Mitchell in the main event on Showtime (9 p.m. ET/PT, delayed on West Coast. WBO junior featherweight champion Joan Guzman is scheduled to appear in the co-feature.