The title of Liam O'Flaherty's short story is basically straight forward. A sniper is a sharp shooter who might perch on high ground in order to overlook the terrain below for enemy activity. In this story, the sniper is protecting Dublin's Four Courts government building which is close by. In the process, he kills two people below him, a woman who is pointing out his position and an armored car commander who foolishly comes up out of his protective cocoon.
The title also suggests a lone and anonymous soldier who carries out his duty in isolation. He is battle hardened and ready to kill in an instant. It is a lonely existence for a sniper who must move in stealth in order to avoid detection. Even lighting a cigarette is dangerous. The sniper's life is described as ascetic, which means he goes without luxuries. He is virtually anonymous. All we know about him is that he is a Republican set against his Free-State opponents. Some of his anonymity, however, is lost at the end when he shows emotion over killing the opposing sniper. This emotion carries over for the reader as it is revealed in the last lines that the enemy sniper was really his brother.