Straight Back? Straight Through?
Simple physics and geometry says no. Putting observations say no. But the mental image of straight back actually helps some players… and here’s why.
Most players don’t actually “do” what they think they are doing. They have a mental image, but the physical reality is something different.
Now, the physics and geometry are this… the USGA sets a minimum limit of 10 degree lie angle from the vertical, for a reason. They do not want a player to be able to swing the putter in a true “vertical plane” with what would be a pure “gravity pendulum” motion. Therefore, the shaft will incline at least 10 degrees from the vertical, placing the hands inside the putter head (towards the player).
This fact, and the fact that the human anatomy results in a likely pivot origin roughly at the spine between the shoulders and neck, means that the pivot plane leans back toward the player, and the putterhead swinging on this plane will naturally swing “inside” the straight line from the target (hole on straight putt) back through the ball.
However… that relative “opening” isn’t really an “opening”. Especially from the view of the player. In fact, the easiest way to understand the player’s view of it, their hands and arms should never manipulate the face angle at all. No “opening or closing” is ever needed. The putterface stays “square” in relative terms, to the pivot.
You just need to allow the structural elements of the posture to control the path and rotation, without “trying” to control the putter in any way. This is why the “grip” we teach, and stance and posture, and the making of a pendulum stroke, is all important. The system of putting with the upper body is what works, every time, if you let it.
We have a different term… one that lets the player focus on what is necessary…
“Let the Putter Swing”