How is the sniper's life threatened?

The sniper's life is threatened when he is targeted by an enemy sniper on another rooftop. He is hit when the other man fires.

Suddenly from the opposite roof a shot rang out and the sniper dropped his rifle with a curse. The rifle clattered to the roof. The sniper thought the noise would wake the dead. He stooped to pick the rifle up. He couldn't lift it. His forearm was dead. "I'm hit," he muttered.