Goal: Connect the trail arm to the torso and bring the elbow down
How to do it
Tuck a towel or headcover under your trail armpit. Make three-quarter swings without dropping it until after impact. Start with half swings and lengthen only when the towel survives 10 shots in a row.
Down-the-line: at the top the trail elbow separates from the side and points backwards instead of at the ground; the shaft goes across the line.
Frequently asked questions
What is the "The armpit towel" drill for?
Connect the trail arm to the torso and bring the elbow down
How do you do the "The armpit towel" drill?
Tuck a towel or headcover under your trail armpit. Make three-quarter swings without dropping it until after impact. Start with half swings and lengthen only when the towel survives 10 shots in a row.
How long does the "The armpit towel" drill take?
About 10 minutes per session, 15 reps.
Sources
David Leadbetter — The Golf Swing
PGA of America — PGA Teaching Manual: The Art and Science of Golf Instruction