If you doubt Bertholy's idea of the trail hands 'retaining' function I just say an instructive exchange with Jack Nicklaus and Gary Player in the opening of Jack's new museum.
Jack points out a photo of himself at '6/100s' (hand at right leg in the downswing) and his shaft is HUGELY bent in what Jack originally thought was the opposite of expected - he expected that the shaft would be bowed down with the club head 'lagging' behind (similar to the shaft in transition). Instead the shaft was dramatically bowed up! This is clearly an indication of the momentum of the club head continuing down against resistance from the hands. Those like petearm who have tried to hold the angle in one handed drills know there is no way the lead hand alone would have the strength to deliver this position. Trail hand at work 'retaining'.
