Hitting the back of the ball instead of the side of the ball. It means starting the ball in the direction you are aiming with a powerful squared up club face.

Edit, OK I looked at your video, can't tell much from the distance and head on view other than you freeze over the ball and tense up, and possible flying right elbow.

Try putting a towel under your arm pits and swing without dropping them, and try to relax. Or my favorite is a rope around your waist and right arm to keep your right elbow down and pinned to your right side.