William and his mother immediately left for Dunfermline, but William insisted that they return to Elerslie where they were from and her family was. After a cunning escape and quietly trudging their way to Elerslie they were met by Margaret's father Sir Ranald. Sir Ranald informed them that the news of Selby's son's death was quickly spreading, and a price had been placed on William's head and he was labeled an outlaw. Not wanting to make life difficult for himself he told them that he could look after his daughter but could do nothing for the outlaw William, his best advice was for them to split up and for William to join his uncle Sir Richard Wallace who lived in Riccarton. After some time William reached Riccarton by February 1292 and stayed there until April.

This uncle is most likely the uncle referred to in the film 'Braveheart'. Uncle 'Argyle' as he is known in the film, was portrayed as half blind, educated in languages, skillful with the sword and a general all round clever guy with a strong will. It is more likely that "uncle Argyle" is a character made up of all of the uncles that William lived with. Two uncles taught him the skills in the church and languages and the uncle he was with now after the Selby incident, Sir Richard Wallace, can be described as having been blinded, disabled and enfeebled through loss of blood in some previous skirmish he had with the English.

Everything seemed quiet and William had found a friend in his uncle's page. It is reported that one day when he was fishing on the Irvine a garrison of English soldiers rode passed. The last five soldiers, who were impressed with William's catch decided that they should have it for themselves. When William exclaimed that the catch was intended for the super of an elderly knight, the English soldiers said that they had their permission to continue fishing in order to catch more. Everything was all very peaceful and when William asked if he could at least keep half of the catch as this would be 'fair', the ring-leader of the five Englishmen became angry at being talked to so familiarly by an upstart Scot; he drew his sword and lunged for William.

William defended the blow with his fishing-pole and struck the soldier knocking him to his feet and sent his sword flying. William rushed for the sword in order to arm himself, he detached the head of the soldier with a hard blow to the neck and turned to the other soldiers who had already dismounted and were making their way to aid their fallen comrade. William's blood was boiling; he hacked one to the collar-bone, another he struck on the arm with such force that both sword and arm fell to the ground. While the other two made off, William quickly finished off the man he had just maimed by running him through with the English sword.

On return to his uncle's house, he explained what had happened and told his uncle that he would leave his home in order to spare him the wrath of the English who would surely be soon on their way. He gathered together his possessions and William and his new page, who would also have been targeted with a price on his head, took to the woods in the north just like his father and brother had done a few years before.

Meantime, John Balliol was about to be crowned and the divide in Scotland was thickening. William was now an outlaw for, what would have been seen as, multiple cold blooded murders. He was an outlaw, a criminal and a man with a price on his head. His family were scattered to various parts of southern Scotland, his father was dead and William had no choice but to fight or die, the penalties for what he had done was death. He was only 20 years old.