Abstract: Employee #1 was using a tapping tool to clean the threads of aluminum forks on a bracket in the shop plunger on an ER-Cella B4 T, 700 ton die cast machine. Another employee was at the control panel using two hands to hold the control buttons that sent the plunger into the machine. As long as he held the buttons, the plunger stayed forward and Employee #1 could better work on the threads. A third employee was bothering these two employees, slapping them with his gloves. During the horseplay, the employee at the controls momentarily let go of the buttons when he was slapped by the bothersome employee. The plunger returned to its original starting position and the bracket caught the arm of Employee #1, pinning it against the C frame of the machine. Employee #1 sustained cuts, bruises, and broken bones in his left forearm.