People are amazingly blind to even bold print in their books. It is an offical variant rule on DMG p28. Bottom right corner.
VARIANT: CRITICAL MISSES (FUMBLES)
If you want to model a chance that in combat a character could fumble his weapon, then when a player rolls a 1 on his attack roll, have him make a DC10 Dexterity check. If he fails, his character fumbles. You neeed to decided what it means to fumble, but in general, that character should lose a turn of activity as he regains his balance, picks up a dropped weapon, clears his head, steadies himself, or whatever.
Fumbles are not appropiate to all games. They can add excitement or interest to combat, but they can also detract from the fun. They certainly add more randomness to combat. Add this variant rule only after careful consideration.
