Chainsaws can be dangerous beasts. I know 2 guys that had run ins with them and in both cases the saw won. One fellow I worked with had a nasty scar that ran from his forehead to his waist. One day I asked what happened. He told me he and his brother were building a corn crib. When they put the roof boards on, they left the ends unfinished with the intent of cutting them all the same length with a chainsaw.
He climbed the scaffold, started the saw and began cutting. Just then the scaffold collapsed, and he went flying. The saw followed him down bouncing off him as they fell. It cut from his forehead to his eye, skipped over the eye and cut from just below the eye to his waist. In all he had over 300 external stiches, and several more internal stitches.
In another incident the brother of an ex-girlfriend had an encounter where he was cutting down a tree in a fence row. In this case the tree had grown around a steel fence post. He was about 6" into the tree when the saw kicked back and hit him in the face. It made quite a gash and left a scar from below his left eye to his chin.
I've always had respect for those saws and try to be extremely careful when using them but unfortunately even the most careful people can get injured through no fault of their own.