Quick answer: At the top the shaft goes clearly past horizontal; the lead arm bends and the grip loosens at the end of the backswing.
What it does to the ball
The downswing starts from a different place every time: wide dispersion and irregular contact, with no real distance gain.
Root causes (by frequency)
Chasing distance by lengthening the backswing instead of turning better
A trail elbow that flies open and loses structure
A grip that opens at the top
How to fix it
Backswing to 10:30 with a firm lead arm: what matters is the full shoulder turn, not the length of the shaft
Drills that fix it
Top at 10:30 · 15 min · 20 reps
Shorten the overswing without losing shoulder turn Record face-on and swing back only until your lead arm reads 10:30 on the clock. Check on video that the shaft doesn't go past horizontal. Once you nail 8 out of 10, hit balls at 80% with that stopping point.
Frequently asked questions
What is "Overswing (past parallel at the top)" in the golf swing?
At the top the shaft goes clearly past horizontal; the lead arm bends and the grip loosens at the end of the backswing.
What does overswing (past parallel at the top) do to the ball?
The downswing starts from a different place every time: wide dispersion and irregular contact, with no real distance gain.
How do you fix overswing (past parallel at the top)?
Backswing to 10:30 with a firm lead arm: what matters is the full shoulder turn, not the length of the shaft