As I’ve said, the right forearm and trigger finger control the plane of motion by tracing the baseline of the plane – normally the target line – through impact. The forefinger senses the pressure created by the drag of the lagging club (specifically, the sweetspot), and it directs this lag pressure feel directly toward and along the line. Meanwhile, the left wrist remains perpendicular to the ground. It appears to roll through impact, but it is not independently twisted. Because the left wrist does not swivel – again, it simply remains perpendicular to the ground – the clubface closes uniformly. It does not over-roll and, and unless otherwise intended, it does not lay back. So, control of the clubhead orbit and lag pressure is a right hand function. Control of the clubface is a left hand function.
Perpendicular to the ground? Isn't that only with vertical hinging?