I was going through my old posts on HSM Meta and found this one in which I had informed about a user getting the Citizen Patrol badge without them even having the minimum requirement of 15 reputation for flagging a post. The moderator's reply to my query was that:
Under certain circumstances a new user is able to flag posts with less than the required 15 reputation. In this instance the user in question did indeed submit a flag. You can even see from their profile that they have 1 helpful flag. (The flag wasn't yet handled when this question was posted but has since been dealt with.)
So, under what circumstances can a user flag a post without them having at least 15 reputation? I tried finding such a post here but could not see any post regarding it. Such information may help a lot of new users who want to contribute constructively in their initial days on SE.