Employees were unloading a flatbed truck in the laydown area of the job site. An operator picked up a piece of pipe with a telehandler to unload it. Another employee signaled the operator to lower the pipe down onto the truck to readjust the straps. When the tie down strap released, the pipe rolled and struck an employee's lower right leg fracturing it. The load also struck another employee in the lower back. Both employees were knocked off the truck by the rolling pipe.