A little boring...
It's silent. You really want to put some sound effects in to make it more interesting. It's also not very dramatic or realistic. Try adding a background. If you want to keep the frame-by-frame style, you don't have to redraw the background again and again. Just make it a symbol with two different but similar frames. But you probably already knew that. Anyways, next time make the movements more dramatic. Have the guy get bowled over by the rock, rather than leaning to the side after he's hit. Maybe add some blood?
I don't know. keep up the good work.