hammer (away) at someone
Fig. to interrogate someone; to ask questions endlessly of someone. The cops kept hammering away at the suspect until he told them everything they wanted to know. They hammered at him for hours.
hammer (away) at something
1. Lit. to continue to do a task that requires much hammering. The roofers are hammering away at the job, trying to finish before night.
2. Lit. to pound at or on something, such as a door. Who is hammering away at the door? The police are hammering at the door.
3. Fig. to dwell overly long on a point or a question. Stop hammering away at the same thing over and over. The agents asked question after question. They would not stop hammering at the issue.