Apparently I need to do ten of these for the Mercenaries Guild but the game seems to have forgotten to explain what it is. I've tried grabbing guards with the hookblade and then throwing them, and I've tried the running move (that replaces tackle) where you run into someone, hookblade them, *throw* them to the ground and vault over them (the challenges FAQ seems to be suggesting that this is the correct move), but the hook-and-throw count is still at zero. What's the deal here?
You cannot grasp the true form of JD Fedule's signature!
Well, a hook-and-throw is a move which consist basically of two parts, the hook and the throw.
You are most likely performing a Hook-and-run instead of a hook-and-throw. Like Maturin said, one is performed by holding the B button while the other is performed by just tapping that button. I can't remember which is which, though.
Senkou is correct. There are three counters to a normal enemy attack now: Counter Kill (X) Counter Steal (Y) - No damage, but loots the enemy where they stand and allows you to chain a kill streak off of it. Hook and Throw (B) - Really just the same thing as Counter Kill, except it permanently incapacitates them instead of killing them. You might also be able to throw the enemy into another enemy; I'm not sure about that.
In the modern world, "common sense" is an oxymoron.
That Counter-Grab move is not the Hook-and-Throw as far as I know.
I didn't know about that counter grab -I just tried it out a few minutes ago, it's awesome by the way- but I had completed the Hook-and-Throw and the Hook-and-Run challenges long before knowing that move, so definitely is not that.