Yes, as Shrike said you are missing important frames. My post shows an example of a walking animation, but the idea of each frame translates regardless. The recoil frame is the frame that makes it look like he is actually impacting the ground, not just kicking his legs back and forth. Also, as I already said, try making it 8 frames. It will be difficult to make something that looks good with fewer frames then that, and for your first try don't burden yourself with that challenge.