Well, not very often… the double weak position. Corey Pavin I think has the weakest combo I have ever seen and he is a great ball striker… but not a long hitter.
Nothing wrong with having the left thumb slightly down the right side of the shaft (looking down at it). Mine is about 2:00.
The calluses on my right hand are on the two middle finger pads near the top (toward the finger tips) with a slight one on my index finger in the same relative position. I am not super weak with my right hand, but certainly not strong.
Sorry, after re-reading what I wrote I can see where I gave the impression that the left thumb supporting the shaft is a bad thing. It’s not, the left thumb should support the shaft. However, in the context of what Prot was describing…it sounded like he wasn’t using his hands correctly in module #1. Doing the reps, not making the proper motion with the hands. The thumb should support, but never hit. In the P3 “transition” the support from the left thumb changes to the rotation of the left hand and a support/strike with the right.