Combat Moves

I had an idea this morning - it needs to be fleshed out a bit more, but I think there is some merit.

When a character hits a target, but before they roll damage, they can declare how many points of damage they would like to convert into a control move. A control move is something like "disarm the target" or "shove them into a spiked  wall". Damage dice are rolled and any control move points are removed from the damage.  If the character still managed to cause any damage to the target (past DR) then the target must pass an opposed roll to avoid the move.

Example
Bill the barbarian attacks the Hyperghoul trying to eat his face.  Bill hits, and before he rolls damage he declares "3 points to knock the ghoul prone".  If the damage roll is less than 5 (the hyperghoul has 1 DR) then nothing happens.  If the damage roll is 6 or higher, the ghoul takes a bit of damage and a potential knockdown.  Bill rolls 2d6+3 vs the GM's 2d6+1 (the +1 from the monster's danger value / 3 as standard for all non-specific monster rolls). If Bill is successful, the hyperghoul is now lying on the ground.

The specific effects of a combat move may need to interpreted by the GM. The GM of course can add bonuses to things - knocking down a large target is harder than a medium one, and shoving a rhino is pretty unlikely.