6-A-4. Arms. "It is important to keep in mind this 'normal' position of the Arms - that until after the Follow-through, the Left Arm is never bent, and the Right Arm is never straight. The Left Arm bends if and when it is carried - NOT THROWN - closer than about 45 degrees to the Shoulder line. (See 6-B-3-0-1.)"
The Left Arm is kept straight due to Extensor Action, 6-B-1-D. It is in effect from Impact Fix to the end of follow-through. Two of the four things it promotes are: 1. The full extension of the Left Arm at all times, and 2. The full extension of the Right Arm for follow-through.
As for the Left Wrist, 4-D-0: "Normally, only Swingers with their Standard Wrist Action (10-18-A) 'Swivel' - that is actually rotate the Left Wrist - through Release into its Vertical Position for Impact." "But all players must 'Swivel' - actually rotate their Wrists - into the 'parallel to the Plane' position for the Finish (8-12) after the Followthrough."