Jack, most Pros have that stiff front leg like you showed Bonds. I know if if don't have a stiff front leg like my son had trouble doing before that he would get out over his front leg which would lead me to believe the weight transfer was trying to happen. In my honest opinion, that is my you should have the stiffer front leg to stay back and then cause the same affect a car has to your bondy when you slam on the breaks and if you don't have a seat belt your momentum will take you forward. So doesn't that front leg act as the break of the transfer cause your rotation of the hips.shoulders to fire through ?? Just me thinking out loud and wanted to see if I am way off base in my thinking
You state, "cause the same affect a car has to your bondy when you slam on the breaks and if you don't have a seat belt your momentum will take you forward." -- You are correct. Therefore, the driver's linear momentum is expended straight into the seatbelt, which did not induce his body to rotate. The same is true with a batter's hips. His linear momentum is expended straight into his lead-leg and ground before hip rotation starts.
As the video clip below illustrates, there is no linear movement and rotation taking place at the same time.
Linear momentum is expended (forward motion = 0) before body rotation is initiated.
Giambi - Momentum & the lead-leg