Bonds movement allows him to fall into both legs without compromising the rear leg/hip relationship..
This is another example of riding the rear leg that I am referring to...
Does Bonds stride get longer for off-speed while riding/gliding out ?
https://twitter.com/uTeeBaseball/status/830883285903499264
My 2 cents. I feel Happ's over rotation of the lower body affected his ability to lower. Why did he over rotate, probably fooled pitched ball speed.