.

.

Swing your club to the top of your backswing. If your right arm (right-handed player) forms a perfect right angle, chances are your left arm is
in a relatively extended condition.
This is an example of a good back-
swing radius. Radius, in fact, is a speed source. Try again, only this
time purposely cause your right arm to completely collapse. Notice now that your left arm also now sags.
The radius of your backswing is almost non-existent. The right arm should structure the left in the backswing.

.

.