Here, I've been mucking about with the angle of the hips and chest to try and smooth out some of the animation — most notably just as he leans back into the contact pose. I've dropped the hip to the side, in favour of the 'pushing' leg on the up pose to try and give a bit more feeling of shifting weight. I've also curved the hips backward and tilted the chest just slightly forward to try and offset things a little.
The biggest issue, as you'll see from the perspective view, is due to this alteration in the hips his knee now trembles and shakes all over the place. I have no idea why it does that and I'm trying to fix it by manually keyframing the up vectors, but for some reason it just won't stick... it'll tremble between keyframes and then snap to the keyframed position. I have no idea what the heck I'm doing!