Well, Hammer, I asked the same question. I was told that NWHS takes in most of the City kids that have access to Rec soccer and organized club teams whereas RHHS has a less urban population and few soccer opportunities are available to them, assuming there is a family interest in the sport to begin with.
If I have mistated the case, you Rock Hill people please give us the real scoop. I'm just passing along what I heard from one Rock Hillite.