I'm afraid I can't see that happening in most places. Even a pub brawl in the outback, which would otherwise be inconsequential if unreported, would result in at least some degree of investigation if reported to police.
In Australia if a crime is reported, and even the perpetrator arrested, a brief is prepared and submitted to a senior officer who must decide if he believes there is sufficient evidence to secure a conviction. If not, charges are dropped, often to the consternation and anger of the victim. That way many hours of police time are not wasted preparing cases that will never get a conviction.
If someone was knocked out and maybe injured, I believe there would be no police 'doing nothing'.
:asian: