I'm not sure if this has been posted before, but does the lead leg need to be bent for any reason? Bauer, Chapman, Lincecum, and the Japanese pitcher all straighten their lead leg upon descent, which appears to function in two key ways: allowing the weight to sit on the drive leg and enabling the hips to lead the way and dominate the delivery rather than the lead leg. If you straighten out that leg, it is literally impossible to generate any momentum from it as all the focus shifts to your drive leg (Go ahead and try it!). When I've tried this, the lead leg really comes along for the ride and the hips take over, so long as your lead leg straightens before it breaks the plan of your front hip.

What's everyone think about this?

Also, an observation: compare the Japanese pitcher, Bauer, and Lincecum. The Japanese pitcher is completely linear with his hips and lead leg. Bauer lifts his front leg up and his hips rotate his lead leg back. Lincecum rotates his lead leg way back, but still (possibly because he straightens his lead leg?) gets his hips going first. Three different styles, but all straighten that lead leg with excellent force vectors, hips leading, and keeping the weight back into triple extension.