Careless alignment (body and face aimed at different spots)
Quick answer: Down-the-line: the lines of the feet, hips and shoulders are not parallel to the ball-target line; the shoulders usually end up open.
What it does to the ball
The path follows the shoulders: open produces out-to-in with a pull or slice; closed, a push or hook. Dispersion doubles without the swing changing at all.
Root causes (by frequency)
Aiming the body at the target instead of parallel left of it (railroad-track effect)
Not using an intermediate target when setting up
An inconsistent address routine
How to fix it
Pick an intermediate target 20 inches in front of the ball: align the clubface to it first, then build your stance parallel
Drills that fix it
Railroad tracks · 15 min · 20 reps
Align body and face the way the pros practice Put one stick on the ground pointing at the target just outside the ball, and another parallel along your foot line. Hit balls checking that shoulders and hips follow the foot stick. Remove one stick every 10 balls to wean off the aid.
The target half a meter away · 15 min · 20 reps
Automate a reliable alignment routine for the course From behind the ball, pick a leaf or blemish 20 inches ahead on your line. Align the clubface to that spot first, then build the stance. Do it on every ball in the bucket without exception, as a complete routine.
Frequently asked questions
What is "Careless alignment (body and face aimed at different spots)" in the golf swing?
Down-the-line: the lines of the feet, hips and shoulders are not parallel to the ball-target line; the shoulders usually end up open.
What does careless alignment (body and face aimed at different spots) do to the ball?
The path follows the shoulders: open produces out-to-in with a pull or slice; closed, a push or hook. Dispersion doubles without the swing changing at all.
How do you fix careless alignment (body and face aimed at different spots)?
Pick an intermediate target 20 inches in front of the ball: align the clubface to it first, then build your stance parallel
Sources
Harvey Penick — Harvey Penick's Little Red Book
David Leadbetter — The Golf Swing
PGA of America — PGA Teaching Manual: The Art and Science of Golf Instruction