Injured riding in Damascus Mac 12 Mantrip traveling out of the mine at quitting time. The mantrip pulled over to the side to allow a Johnson Mantrip to pass by. When the Mac 12 inadvertently brushed a coal rib an Ocenco SCSR Storage Box came up out of the 2"" channel brackets holding it in place. The SCSR Box rolled over striking the injured's right lower leg causing a laceration.