The degree of hematuria does not corrolate with the degree of damage to a kidney from blunt force trauma, so yes, he could have visible blood with or without little tiny skinny worm like clots even for a couple days. Microscopically, the blood would be detectable for about 6 weeks. It will be more visible with fewer urinations such as if he's dehydrated or first morning urination. Evaluation would be a CT scan without and with IV contrast to rule out a renal fracture and assuming it's non surgical which is common for blunt trauma, treatment would be hydration to keep the tiny clots from obstructing the flow of urine from the microscopic nephrons to the macroscopic ureters and avoidance of further trauma (rest, but not true bedrest), Acetominophen and opiates for pain, Aspirin and Ibuprophen-like products are a bit more controversial but used to be the mainstay a few decades ago. Some Urologists like that they thin the blood a bit, and others are frightened by it. In a low tech or no doctor environment, light beer alternating with lemonaide for pain relief and hydration would be a reasonable approach.
A punch to a kidney however is no more likely to result in incontinence as pain inflicted anywhere else.
