Originally Posted by dougdirt
They do also call it a spike curve. Its all about the grip. You use your index finger on the seam like you would grip a knuckle ball (shown to me by Phil Hughes of the Yankees - Name dropper).
Side note though is that Sean Watson actually stopped throwing the knuckle curve for a while there because he couldn't throw it for strikes at all. Once he left Dayton hitters figured out he couldn't throw it in the zone and they stopped swinging at it. He is throwing a curve again, but I am not sure if its still the knuckle curve or not.
Judging by the incredible spike in walks, I'd guess that he's throwing it again.