If It were me, I would make him sign, I would have made the police sign a statment saying that they were aware that my suggestion was that he get medical treatment and that I had advised them all of the dangerous nature of head injuries.....If the completely refused transport after medical advice then he would be really dumb not to get a release, because he is responsible if something happens once he has initiated care.
The only way that I would NOT have them sign that relase would be if the injuries were of a superficial nature and I had no suspcion that anyone had had head trauma My own personal feeling is that the injuries could not have been much more than superficial if he went to the Police Station rather than to the hospital....a good thump on the head is usually preseaged by severe nausea, and a whopper of a headache, let alone how hard it is to talk with your face all swollen from a broken nose, a lot of times your eyes swell shut, and usually you can only breathe through your mouth till some swelling goes down, yet in this condition he wanted to go to the Police station instead of the Hospital....I am less than convinced..