An over the top golf swing is experienced during your downswing.
As you swing the golf club back down towards the golf ball, if you look at your swing from the side you would see that the club head moves over the top of your hands and towards the target line. The result of this movement is that the club head will now move to the far side, or to the outside of the target line and for you to hit the golf ball from this position you will now need to pull the club head towards you and across the target line to the inside of it, or the side that you are standing on.
This movement is caused by rotating your upper body to initiate your downswing rather than rotating your lower body first. As you turn your shoulders towards the target, the club is thrown forward and over your hands and it becomes very difficult to hit straight golf shots at the target.
To correct this movement and to improve your accuracy with hitting golf shots at the target, work on the following golf drill. Set up ready to hit your golf shot and then place a range basket about one foot to the right of the golf ball, if you are a right handed golfer, and about two inches on the far side of the target line. You should be able to swing your golf club away from the ball without hitting the basket but the club head should only just move inside the basket.
On your downswing, work on turning your lower body towards the target first, Turn your knees then your hips and then finally your upper body and shoulders towards the target and swing the golf club down on the inside of the basket to strike the golf ball. Do this slowly at first and as you become better with the movement gradually build the speed back into your swing but make sure that you keep the club head on the inside of the range basket as you approach the golf ball.
Working on doing this will get you swinging the club head from along the target line and will prevent you from making the over the top movement, which would result in the club head striking the range basket. With the club head moving along the target line if you keep the club face aiming at the target as you do this, you will begin hitting straight golf shots which will really improve your accuracy the next time you are out on the golf course.