Back to Campbell Clinic in Memphis went U. of Kentucky center Sam Bowie and his fractured left shinbone, and on went a new cast, for six weeks. So, while the doctor said, "Sam's leg looks a great deal better; the new cast will be such that he can exercise the leg (on which he had a bone graft Oct. 20)," it's virtually certain: wait till next year for Bowie and UK Coach Joe B. Hall . . . Calling Bob Knight an "ugly American," Gov. Carlos Romero Barcelo of Puerto Rico carries on campaign to remove Indiana's Knight as U.S. 1984 Olympic basketball coach with an "adamant protest" by letter to the secretary general of the U.S. Olympic Committee . . . Landover 1, Louisville 0: While Capital Centre gets sales rolling for the 10th Capital Classic April 1, scrub another high school all-star game, the Kentucky Derby Classic. Promoters cite trouble attracting seniors limited by NCAA to two such games . . . .Now, Sugar Ray Leonard, basketball player. The champ's SRL All-Stars, starring himself, to play school faculties to benefit their athletic programs. First outing, tonight, Northwestern High in Hyattsville, fount of all those basketball-playing Spriggses, including Greg Spriggs, Leonard's bodyguard and now teammate. John Love of M-NCPPC's Riverdale office books them.