Interaction Isn't Explicit。

You need to make 7 headshots without missing - that is, you need to empty a full clip. You can do this on one enemy - shoot, he falls, wait for him to get up - repeat the attack. The easiest way to get it is in the first chapter, when you are first given a pistol. There will be an enemy who does not attack you, so you just put him down 7 times and the trophy is yours.

A buggy trophy, on one account when I killed a dozen enemies with a headshot + finishing blow to the head it still didn't give me the trophy, but on the main account it did the first time.