RDU spokesperson Mindy Hamlin said there had apparently been an earlier disagreement between the attendants that escalated when one accidentally brushed the other.
The captain of the plane brought the aircraft back to RDU and requested to be met by law enforcement.
Investigators determined no blows were exchanged and no assault had taken place. There were no arrests.
Hamlin said United Flight 1214 left the gate at 6 a.m. and returned at 6:40. Seats on other flights were found for passengers.