For many casual fans, the annual Christmas Day marathon marks a sort of unofficial beginning to the NBA season, the time where non-diehards start to turn attention from football and the hot stove to the stuff we've been watching for the past two months. When all those eyeballs focus on ABC and ESPN this Friday, they'll see something new that's got nothing to do with the action on the court — an advertising campaign featuring NBA superstars calling for an end to gun violence, the product of a partnership between the NBA itself and what The New York Times calls "one of the nation's most aggressive advocates of stricter limits on firearm sales." [ Don't miss Yahoo's NBA free roll on Christmas. Join our $25K Stocking Stuffer Contest ] Four NBA players — reigning league Most Valuable Player Stephen Curry of the Golden State Warriors, eight-time All-Star Chris Paul of the Los Angeles Clippers, 10-time All-Star Carmelo Anthony of the New York Knicks, and two-time All-Star/former Defensive Player of the Year Joakim Noah of the Chicago Bulls — appear in the first 30-second spot, which will reportedly air five times on Friday, during the NBA's Christmas quintuple-header...