Y
The back leg reacts to the hands. Most pros try to maintain the back leg. They don’t try to activate it. Usually only when it’s a lower pitch.
A
Again don’t understand how you can’t see that the back leg is starting at the same time as the hands TTB where you abduct the back arm. The hips are still coiled, but the back leg is starting at the same time. The back leg starts on every pitch, unless it’s an obvious ball. Otherwise you’re not ready to swing.
The back leg reacts to the hands. Most pros try to maintain the back leg. They don’t try to activate it. Usually only when it’s a lower pitch.