Fifth Element
Legend
Not sure about that. The last paragraph of the Sneak Attack description says "A rogue cannot sneak attack while striking a creature with concealment or striking the limbs of a creature whose vitals are beyond reach."What no rule does this. Houserules maybe, but RAW disagrees. Legs have sneak attack point areas.
So, no hard-and-fast rule about what creature have vitals that are out of reach (I'd say a Large creature's vitals are generally still within reach of a Medium creature), but no, legs do not have "sneak attack point areas." Unless the creature has vitals in its legs.