The specific risk of assembly instability during torque application was not fully identified during the planning phase. The chain tong and pipe wrench was in good condition, and no defects were reported. The assembly was placed on a wooden base, which did not provide stable support on both sides. The chain tong slipped, releasing uncontrolled energy, which caused the assembly to rotate and fall onto the roustabout’s leg. A Toolbox Talk (TBT) was conducted before starting the job, and the Driller and Fishing Engineer supervised the task. Stop Work Authority was not exercised when the roustabout was standing in the line of fire, and no intervention occurred until after the incident.