The documentary Audience Award winner at this year's Sundance festival, Buck follows itinerant horse trainer Buck Brannaman as he applies his uniquely humane and frankly astounding methods in four-day clinics around the country. If that sounds as exciting as watching hay turn yellow, director Cindy Meehl finds the real story in Brannaman's fractured past as a child celebrity trick-roper who, along with his older brother, Smokie, was systematically abused by their alcoholic father. Despite these odds, Brannaman grew into a preternaturally gentle adult who channels hard-earned patience and compassion into his work. You can hardly blame him if he plays to this narrative hook with a showbiz veteran's skill, and Meehl — whose documentarian's reserve is impressive for a first-time filmmaker — generally resists identifying too closely with her subject. She gets candid comments from Brannaman's associates and childhood friends as well as Sundance sultan Robert Redford, who employed the horseman for his 1998 adaptation of The Horse Whisperer. Lest Buck get too clubby and touchy-feely for its own good, Meehl closes the film with a sobering last-act scene in which the trainer encounters a raging, haphazardly reared colt even he can't reach. It's a subtle and harshly evocative reminder of how differently his life could have turned out. Not rated.