Hi The most common localized bump after injury is due to blood and fluid collection within the skin. This produces a bump with discolored skin above it sometimes without pain too. It will take around two to three weeks for such a swelling to come down. So, if your friends bump is looking like one, try cold compresses with ice pack and an antiflammatory drug like a dose of ibuprofen twice a day after food for three days, until you get an appointment with the physician. A physicians consultation is required to rule out any fracture associated (detected by X-ray or CT Scan)and the intervention needed accordingly. You might need an antibiotic too (as precautionary measure)as hematomas are prone for infections. But confirm it with your doctor.