...the No Sunday Play exception that BYU (and Campbell University) request whenever they qualify for an NCAA Tourney that would have a game scheduled on Sundays.
http://magazine.byu.edu/ncaa-changes-sunday-competition-policy/
After the linked article was written, BYU did, in fact, get the needed 100 schools to request an override vote; which subsequently restored the rule colloquially known as "The BYU Rule"