In the center is Charles James II, who seemingly should be on the outside looking in. As the Giants defensive backs come off the field and huddle for some post-practice inspiration, there’s a galaxy of stars encircling James. First-round draft picks (Antrel Rolle, Dominique Rodgers-Cromartie, Prince Amukamara), Super Bowl champs (Walter Thurmond) and interception kings (Stevie Brown) all lean in and listen intently as James — undrafted, undersized and largely unknown — chants, dances or otherwise gets everyone’s rapt attention. “Yeah, Charles James II is always a great time,’’ Amukamara said, smiling. Everyone gets a kick out of James, but he won’t stay around for his entertainment value. He’s in a dogfight to hang on to his roster spot, as the Giants revamped their cornerback position by signing Rodgers-Cromartie, Thurmond and Zack Bowman, veterans owning sizable NFL résumés. Amukamara is a proven starter and Trumaine McBride, coming off hip surgery, has put together so impressive a summer Tom Coughlin says, only slightly exaggerating, “He intercepts a ball and goes 80 yards every day.’’ There’s more. Bennett Jackson, a rookie sixth-round pick from Notre Dame, looks rangy and has potential, and then there’s Jayron Hosley, a 2012 third-round pick who hasn’t developed as expected and is suspended the first four games of the regular season for violating the NFL’s policy on illegal drugs. It’s a great deal to sort through and there is no time for James to falter. He came up with an interception in Thursday’s practice and figures to get significant time in Saturday night’s preseason game against the Steelers at MetLife Stadium.