Crier haro sur quelqu'un = To raise an outcry against any one.

[“À ces mots on cria haro sur le baudet.” LA FONTAINE, Fables, vii. 1.

The origin of the word haro is disputed; Littré quotes Diez, who connects it with O.H.G. hera = here. The old opinion was that it was derived from Ha-Raoul, an appeal to Rollo, or Hrolf, first Duke of Normandy, and a mighty lawgiver. However, within living recollection the cry of Ha-Ro! à l'aide, mon Prince! was used in the Channel Islands as a protection against force and fraud, when no other defence was possible. See a curious tale in “The Gossiping Guide to Jersey,” by J. Bertrand Payne, London, 1863, p. 15.]