I have a story just like Bob's, one guy working for the woodland crew for Parks, cutting low on a small tree with a long bar swiveled the bar around the far side of the tree and just nicked the back side of his left leg, another in the Regiment did almost the same thing...they wer both wearing chaps
Bob's right, if you contact the front of your leg, the chain can pull the protective clothing around and swivel and before you know if the side/back of your leg is NEKKID!
I always go for wrap chaps or class A trousers that have lower leg protection, the Cloggers I have are front protection from teh waist to the knees then all around from the knees down,