If the arm swing keeps going after the shoulder turn has finished, the arms can get stuck behind the body during the downswing. This guy is guilty of that. I'm working on lessening my right arm bend to keep the arm swing shorter.
Ball starting at target and curving right = clubface pointed at target and path left of target. Assuming you are hitting the ball in the center of the face.
Golf Pride website has a measurement tool to see if you need larger grips.