Major League Baseball pitchers Tim Wakefield and Phil Niekro talk about being some of the few pitchers in the entire history of baseball who mastered the art of the knuckleball, a pitch so slow and unpredictable that no one trusts it. They’re joined by Ricki Stern, director of the new documentary “Knuckleball,” which follows the Major League’s only knuckleballers in 2011, Boston Red Sox Tim Wakefield and Mets pitcher R. A. Dickey. “Knuckleball!” is playing at the IFC Center.