Punched a person & car window about two weeks ago. X-rays show no fracture. There's a lump on the backside of my hand. Painful to move hand& swollen.

Pretty Handy. More than likely, your hand has suffered some soft tissue damage. If the x-rays were taken immediately after the altercation, a stress fracture may has been unable to detect at that time. This could contribute to the swelling you are having now. It may be to late for the therapeutic effects of RICE now. (Rest, ice, elevation and compression.) You can try moist heat. See a doctor if no improvement.