An employee was cutting up a large tree that had blown down on a rocky ledge on a hill. He began cutting on the uphill side of the tree, but due to obstructions he had to move to the downhill side. The tree separated from its 7-foot root ball, which started sliding toward him. While attempting to get out of the way, he tripped and fell to the ground, striking his head on an unknown object. As the root ball continued to move toward the employee, he made it below the level of the rock ledge. The root ball rolled over when it reached the ledge and pinned the employee's lower leg, and broke his fibula. He also suffered scrapes and bruises from the fall.