In curling, the hack is the push-off point for releasing a rock. The hack is located in the out of play area behind the house, at each end of the sheet. It is made of small pieces of rubber set into the ice. The curler pushes out of the hack from a crouched position, weight on their sliding foot, and glides down the ice toward the hog line, pushing the rock in front.
Many players clean the bottom of the rock while they set up in the hack. If you do this it is important to sweep any debris out of the hack.
It is an informal responsibility of the Lead to set up the Skip's stones in the hack for him or her. The Skip is considered to be too busy thinking of strategy to bother with such mundane chores as fetching his or her own rock.