Q: When shooting a jump shot, should the arm be fully straight?
A: Yes. When you extend the arm fully at the same speed and force (with relaxed wrist and hand), you have a "repeatable" motion. That's what you want. If you short-arm the shot, stopping short of fully straight, then you're adding variables. You want to minimize variables. The straight arm and the flopping or bouncing hand are, to me, the signs of a good shooter. And if the hand stays pointed directly in line with target in the Follow Through, that's a sign that the shot's going to be pretty accurate.