Abstract: At 9:00 a.m. on January 27, 2021, an Excalibur Well Services Corporation crew was servicing Well 221X at a Seneca Resource Well Site lease in Lost Hills, CA. Employee #1, a floorhand, was working on the crew during the operation of removing the pumping unit head in preparation to remove the sucker-rod string. The operator lifted the blocks to raise the rod elevators, which caused the rod string to spin and tangle the lifting slings and bridle. Employee #1 placed a pipe wrench on the rod string and attempted to untangle the equipment. As the rig supervisor approached, he shouted for Employee #1 to stop, but the employee did not respond. As Employee #1 continued to work with the wrench, stored tension in the rods released, causing the wrench to be pulled from the employee's hands. The wrench spun around and struck Employee #1 in the back of the head, knocking the employee to the ground and causing serious injury. Employee #1 sustained lacerations, skull fractures, loss of consciousness, and a traumatic brain injury. The employee was transported to the hospital for admission and treatment.