This drill helps players who keep their right elbow too close to their body at the top of their backswing. This fault causes your swing to lose width (a key factor in creating power) and your muscles to tense up.
Place a headcover in the armpit of your trailing arm as shown in the image (sort of). The headcover will lock your right arm in place during the first part of your backswing helping you to maintain the ideal ‘triangle at address’. Start swinging back, letting the right elbow slowly move away, but not so much that it starts to ‘fly’. If you make the right move at the top of your backswing, the headcover should fall out. If it doesn’t, you’ve tensed up and your swing width has been drastically reduced, much like your power. Remember that the headcover should fall out at the top of your backswing, any earlier and your arms are separating from your body too soon.