I talk to a lot of MLB pitching coaches and every one says that pushing off the rubber is a big myth. Yes the leg colleses but if it was pushing off it would straighten out again. The back leg has a part in the forward motion but it is a huge mistake to tell a pitcher to push off the rubber. I have several analysis of Tims motion and he doesn't push off the rubber.The power is delivered out front when his upper bady uncoils. I used to pitch Fast ball and you would think that you push off the rubber. Not even close. It was my front leg that took the punishment. When I finished a game my front leg was usually sore because it set up the release of my power as it straightened out. I also pitched BB as well and neither leg really felt sore after a game. My post foot collapsed, my hips rotated and my weight was back supported by the read leg. When I started forward the front leg was bent back and as I uncoiled the rear leg dragged slightly allowing me a stable base for the release of my power as the upper body did its thing. The front leg took the brunt of the pressure. That doesn't mean the back leg didn't play into the throw but it didn't push off. Tim accually reminds me of a fast ball pitcher with his gigantic stride. He also wraps back more than most because he is extremely flexible.