THE INJURED WAS PREPARING TO INSTALL THE 1ST BOLT OF THE 4TH ROW OF THE 9 RT PLACE. WHILE MOVING THE HEAD, A ROCK MEASURE 5 FT CAUSE FELL OUT BETWEEN THE CANOPY AND T BAR AND RIB. THE ROCK STR IKE THE CANOPY AND SLID INTO THE BOOM AREA STRIKING THE INJURED IN THE LEGS. THE IMPACT BROKE THE LOWER LEFT LEG.