It didn't really make sense as a rule, as its only result was to make the league less competitive against others. The thought was that you wouldn't have conference members poaching from each other's rosters... but when teams from other conferences could still do it, it didn't make sense to tell players "you can't go to a school in our conference, but can go help others build up their talent base." Here's the release:
theacc.com
ACC Eliminates Intraconference Transfer Rule
GREENSBORO, N.C. (theACC.com) –The Atlantic Coast Conference announced Monday the elimination of the league’s intraconference transfer rule.
theacc.com
