"A walled field was once reportedly set up in the great square before Notre-Dame cathedral for a duel between a man and a dog. The story goes that in 1372 a nobleman, one of the king's favorites, was found murdered on his estate near Paris. The murder remained a mystery, until suspicion was aroused by the fact that the victim's dog, an enormous greyhound greatly devoted to his master, always growled and barked at the sight of a certain man. This man, Richard Macaire, was known to have been jealous of the victim's good standing with the king. When the king learned of the dog's behavior, he took it as an accusation and ordered that the dog and Macaire be set against each other in a judicial duel.
". . . Macaire was armed with a club, while the dog was provided with a large barrel open at both ends in which it could take refuge. According to one account, 'As soon as the dog was released, it bounded towards its opponent without delay, knowing that it was up to the appellant to attack first. But the man's heavy club kept the dog at bay, and it ran here and there around Macaire, just beyond the weapon's reach. Biding its time, turning this way and that, the greyhound finally saw its chance and suddenly leaped at the man's throat, seizing him there with such force that he dragged him down to the ground, forcing Macaire to cry for mercy.' After Macaire was released from the dog's jaws, he confessed to the crime and was hanged at Montfaucon."
From Eric Jager's The Last Duel: A True Story of Crime, Scandal, and Trial by Combat in Medieval France (New York: Broadway Books, 2004), p. 137.