Just looted the martial skill sharp slicing, with the trait cards "Impaler" and "Slicer" and the attack card "Weak Strike" which deals crushing damage. This seems counter intuitive to me.
As it is a lower level version of the skill it comes with just a basic attack as its third slot - I assume that higher level versions will come with the appropriately complimentary attack. (Evidence I have seen with other skills would suggest this to be the case). Gray
If you want to see the sheer overlapping complexity of it all, check out these Martial Skills tables. (Warning: if you don't wanna see every such item in the game . . . )
Ok, just that most of the other skills that have a trait associated with it have an attack that takes advantage of that trait. I guess they figure that the two traits together in a low level skill need a negative to balance them.