First of all, I want to say that this is a pretty good spright. Your shading and colors and shape are all great, though the animation could use improvement. I think the legs should be moved together a bit, right now they are looking a bit detached. Also, in frames 4, 5 and 7, it looks like he is bending his leg backwards, which is why in the animation itself, the frontleg is swinging around. I think you also might want to look at the other parts of the body. His arm is moving in a strange way, almost as if he is punching his stomach. I think instead of changing the angle of the forearm too much, you should change the rotation of the entire arm as he walks. Also, his hair and torso should be moving a little as he moves. There's no reason he should be breathing while idle and not while running.