Lance Hammer's film "Ballast," a critical favorite earlier this year at Sundance, begins with a remarkable shot, one of those shots that stick with you long after the rest of the movie has become a jumbled memory. A boy or young man in a down coat, seen from the rear, walks through the weeds into a flat, horizontal field, probably one where corn or cotton or soybeans are grown. From the coat and the light and the empty field, it appears to be winter, although part of the seductive power of "Ballast" is that elemental questions like where and when go unanswered. As the boy advances, a flock of scavenging birds -- likely a murder of crows -- explodes out of the field, and this almost painterly composition abruptly becomes a chaotic whirlwind.