Topping is usually throwing the club head at the ball. In your case, probably because you feel the need for the club head to catch up or you'll miss the shot... so you throw it. This can be because, since you did not hold the lower body (left hip), everything turned back on the takeaway together (did not get a windup)... and the hips don't turn very far and they're done, but the shoulders turn much farther and needed a head start they didn't get... now the hips start the downswing, but the shoulders/arms have not finished the backswing... so they're now playing catch up. This scenario can lead to throwing the club head. Another reason might be, you are using hands and arms on the backswing to help vs. using the Large Muscles (shoulders), and then all kinds of things can happen then. Using the Big Muscles helps keep the hands/arms in check (more passive).
Move Less ... Get Good! DUPLESSISGOLF