The boundaries of the side walls of the hammer are defined between the disclosed solid lines and the farthest-most shade lines along the side walls. Further, the boundaries of the top wall of the hammer are defined between the disclosed solid lines and the farthest-most shade lines along the top wall of the head. The dash-dash-dash-dash lines are for the purpose of illustrating environmental structure and form no part of the claimed design. The dash-dot-dash lines depict boundary lines of the design and form no part of the claimed design.