Hum. I'm not the best person to offer animation critique but as far as I can notice, during the stop animation the character should trying to counter the inertia of the running movement by throwing some of his weight to the opposite direction (leaning a bit back for instance). Currently, it looks like he's getting electrocuted or something like that.
I'm sorry I can't pinpoint it more precisely, as I'm not a very well trained animator. Let's hope it makes sense to you.
