Which of the following indicates a sledge hammer's head condition that makes it unusable?

A sledge hammer's head condition that makes it unusable is indicated by a crack. The integrity of the hammer's head is critical for safe operation, as a crack can compromise its strength and structural soundness. When a sledge hammer strikes an object, the force is concentrated on the head. A cracked head can fracture further upon impact, potentially causing pieces to break off or even causing the hammer to shatter, which poses significant safety risks to the user and bystanders.

The other conditions listed do not directly affect the hammer's ability to function safely as a striking tool. For instance, a hammer that is too heavy may simply be inconvenient to use but does not make it unsafe. A loose grip can also make it uncomfortable to use, but as long as the head is intact, it can still serve its purpose. A shiny head often refers to use and doesn't necessarily indicate a failure in function or safety. Thus, only a crack in the head invalidates its usability.