What happened? As part of the rig dismantling for rig move / maintenance, the monkey board was disconnected from the mast and was placed on two pipe racks to dismantle MB walkways for moving. The night crew was assigned by TP to execute the task. Each walkway platform has two top and bottom tapper connecting pins. The crew had safely dismantled three walkways and laid them down on the ground. Afterward, the crew was working on the fourth and they continued removing the right top pin once the pins were removed the walkway platform flipped down to the ground and contacted FLM right foot. He was first examined at the rig clinic and then moved into the nearest hospital for further check-ups and treatment. Why it happened/Finding : Walkway was not secured before removing the pin. FLM was not part of the task. He was walking nearby workplace. Workplace wasn't barricaded to prevent unauthorized person from getting closer to temporary NoGo zone. Task Supervisor moved to another task before completing dismantling Monkey board walkway.