A one-piece takeaway causes a fatal flaw in your backswing -- a flaw that can be overcome only by compensations and tinkering.
In every swing, the clubhead travels a much greater distance from address to the top of the backswing than the arms, shoulders or hips do.
That's simple physics. But with a one-piece takeaway, the body turns early, then has to stop and wait for the arms and club to catch up.
When the body has to wait, it tends to tilt towards the target, and the arms move out of sequence and lift.
One simple move to start back will get your swing in sync.
The first thing you should move in your backswing is the clubhead.
With a subtle clockwise rotation of your left forearm, start the clubhead away from the ball, without moving your hands from their address position, and let your right wrist cock.
As soon as the clubhead moves, feel as if you're pushing down on the end of the grip with the heel pad of your left hand.
It should feel as though the end of the grip is pointing straight down before your hands get past the outside of your thigh on the way back.
By getting the clubhead into this position early in your backswing, you're setting your swing up so the club, arms and body can reach the top all at once.
Then you can return the club to the ball on a good path and plane without making any quick compensation adjustments.
Out of Bounds: Like life, golf is about losing everything gracefully.