OPERATOR WAS CHANGING IMPLEMENTS ON SKID LOADER FROM PALLET FORKS TO A UTILITY BUCKET FOR CLEANING PLANT. IT HAS 2 LEVERS THAT CAN LOCK THE BUCKET INTO PLACE. HE WAS SITTING IN OPERATOR'S SEAT & USED HIS RT FOOT TO PUSH LEVER TO LOCK BUCKET. HIS LT FOOT WAS IN SUPPORT ON PART OF THE FRAME, IT SLIPPED & LANDED ON PEDAL THAT LOWERED BOOM ONTO RT FOOT. CONTUSION OF RT FOOT.