I noticed that the damage from hammer attacks which always do at least 10HP of damage is not affected by Nimble.
To my mind this doesn’t make much sense: the idea is that no matter how heavy your armour is, hammer attacks always do a bit of heavy damage, which is cool; but the whole point of Nimble is you’re not relying on armour to protect you, you’re relying on manoeuvrability to cause blows to glance rather than hit square. As such it doesn’t make much sense to me that the guaranteed hammer damage wouldn’t be reduced by Nimble.
Moreover a big part of the balance between Nimble and Battleforged is how they interact with different weapons: Nimble is good vs. hammers (mostly) but bad vs. cleavers, and vice versa for Battleforged. The fact that hammer guaranteed damage ignores Nimble diminishes this a bit to my mind.
My suggestion, which should be easy to implement, is to simply apply the Nimble modifier to this damage as well. So a bro wearing armour with 15 or less Fatigue penalty would only take 4 damage from hammers rather than 10 and so on.