EE was operating the C/M in the #6 (right) entry on the #1 North Section MMU 005-0 right side. While backing the C/M out a piece of rock fell measuring 8"" x5""L x30""w x7"" thick striking EE in EE's lower back resulting in a broken L4 and L5. Along with a fractured pelvis and a slight tear to the outermost spinal area.