A coach can train/coach no more than 8 (SCHSL 75% rule) of their own varsity, high school players. There is no limit to how many players from one varsity team may play club together as long as their HS coach does not coach them. Hence the appeal of the CESA Prep League: nearly entire HS squads can stay together for minimal fees, they can train at fields in their respective cities, and they do not have to travel outside of Greenville for matches.
CESA is trying to target the "classic" level players that are not being adequately reached by the club, or state for that matter, and offer them a cheaper alternative. The growth of this program would pull classic level players away from existing clubs, but such are the winds of change.
