SAN FRANCISCO — In over 30 years of filmmaking, Nelson George has been to a lot of movie premieres. But Sunday night’s advanced screening of the documentary “Say Hey, Willie Mays!” at the Castro Theatre in San Francisco was one-of-a-kind. “This was very different — this was like a home team screening,” said George, the film’s director. “There are laughs and insight and emotion that you’re not going to get elsewhere. We screened it in New York and it was fine, but it wasn’t the same as being in the ballpark.” There was a ballpark feel to the 100-year-old theater on Sunday night for the West Coa…