A few years ago, Gillian Grisman directed a documentary on the life of Robert Randolph. That film, Press On yielded an intriguing musical moment on Friday night in San Francisco. During the evening’s performance by Randolph & The Family Band at the Warfield, the director’s father, celebrated mandolin player and progenitor of Dawg music, David Grisman, guested with the group. Grisman contributed to a few tunes, perhaps most notably, a cover of Michael Jackson’s ‘Wanna Be Starting Something’ (likely a first for Dawg). Randolph & the Family Band are off until a show at the Georgia Theatre on March 29.