If interested folks really examine the Lincecum video clip at this site carefully, you may learn some things that are not necessarily intuitive.
At his starting position, TL’s knee is pointed toward the camera, so it is difficult to see if he has a bend at his knees. However, pause the video and move the slider of your Windows Media Player about 1/3 along the delivery–there you can see his hips/torso have back-rotated to a more closed position. Note, the thigh of his post leg has also rotated back so that his knee is pointing to about SS position. At that point you can readily see the angle of bend in his post leg.
Moving the slider about 1/2 way along, the front hip is 3 - 4 feet in front of the rubber and the post leg still has the same bend in it.
Just past the 1/2 way mark, the stride leg is extending out, about 1 1/2 feet off the ground, and now the post leg knee is pointing directly at the camera because the thigh has begun to rotate open. Is there still a bend in the post leg at this point? You can’t tell because the vertex of the angle (knee) is pointing toward you.
Try a little though-experiment right here: You’ve glued two popsicle sticks together end-to-end fashion to make a model of a post leg with a 150 degree angle in it. Now, hold your creation in the fingertips of your hand and view it from the side–see the 150 degree angle? Good.
Now slowly rotate (or pivot) your sculpture until the “knee” is pointing directly at you. What do you see? Most of us will see a straight line at this point. Does that mean the angle has gone away? No…it means that the sculpture has pivoted to a new position where you cannot judge its angle. Now, keep rotating the sculpture–does the angle reappear? Yes, it does.
Now, back to Lincecum–Move the slider on your media player a little further to the right and–behold!–he’s further into the stride and his post leg has pivoted more toward home plate. Did you see the angle in his post leg reappear? Well, it never went away becuase he didn’t straighten his leg with a “push”.
As his stride foot touches down the post leg is fully pivoted toward HP and you can clearly see the angle in his post leg.
It doesn’t matter if individual MLB pitchers think that they “push” off the rubber. They get it done, but they may not always clearly understand what they do to get it done.