Originally posted by TOG Phanjam:

hi @AllenCecil. As explained in the linked discussion, "fumbling" is basically when you miss. So your attack deals less damage than when you hit your target squarely. The lower damage on a fumbled attack is some percent of the base attack value (sorry I can't remember the exact percentage) and it's referred to as the "fumble penalty".

Your chance to fumble/miss is governed by a "fumble chance" percentage which is hard-coded for all characters in the game (i think it starts at like 20-something %). But there are "fumble chance reduction" affixes that can appear on weapons, or on socketables (which you can install on your weapons), or can be granted by an Enchanter Merchant. I saw only one affix which decreased the "fumble penalty %" as opposed to like 20 affixes reducing the "fumble chance %".