It is clear that the major threat to the Sniper's life in this short story as we are presented with it is the threat of the other unknown sniper who is on the roof opposite where he is based. Note how the Sniper discovers the existence of his enemy. The Sniper shoots the informer and the solder in the tank and then suddenly, he is shot at himself:
Suddenly from the opposite roof a shot rang out and the sniper dropped his rifle with a curse.
The Sniper has just revealed his position to his enemy who has now shot him and successfully managed to wound him. Of course, the rest of the story tells us how this external conflict is resolved as these two snipers duel in a battle of wits for their lives.