"While it's commonly said that defense = zero when running, this is not true. You are much more likely to be hit while running, but the actual game mechanism is that the entire to/hit formula is ignored, and that any attack that can hit will will deal damage.
The difference is that by ignoring the to/hit calculation, factors besides defense, such as Clvl and Mlvl are ignored also. Thus low level monsters that would often miss a naked high level character who was standing still, will usually hit that same character, if they are running (even if they have on heavy armor)."
From the wiki. Also, 1/3rd block chance is correct, capped at 25%.