DRILLER WAS PUTTING A NEW SAVON SUB ON THE ROTERY HEAD. WHILE TRYING TO TIGHTEN THE SUB INTO THE HEAD, DRILLER WAS HOLDING BREAKOUT WRENCH (48"" WRENCH) ON THE SUB AND RUNNING CONTROLS WITH HIS OTHER HAND. WHEN HE HIT THE ROTATION LEVER THE WRENCH KICKED BACK AND SMASHED HIS LEFT INDEX FINGER BETWEEN THE WRENCH AND THE MAST.