One fine day Grettir rode to the West across the ridge to Thoroddsstad, where he arrived about noon and knocked at the door. Some women came out and greeted him, not knowing who he was. He asked for Thorbjorn, and they told him that he was gone out into the fields to bind hay with his sixteen-year-old son Arnor. Thorbjorn was a hard worker and was scarcely ever idle. Grettir on hearing that bade them farewell and rode off North on the road to Reykir. There is some marsh-land stretching away from the ridge with much grass-land, where Thorbjorn had made a quantity of hay which was just dry. He was just about to bind it up for bringing in with the help of his son, while a woman gathered up what was left. Grettir rode to the field from below, Thorbjorn and his son being above him; they had finished one load and were beginning a second. Thorbjorn had laid down his shield and sword against the load, and his son had his hand-axe near him.

Thorbjorn saw a man coming and said to his son: "There is a man riding towards us; we had better stop binding the hay and see what he wants."

They did so; Grettir got off his horse. He had a helmet on his head, a short sword by his side, and a great spear in his hand without barbs and inlaid with silver at the socket. He sat down and knocked out the rivet which fastened the head in order to prevent Thorbjorn from returning the spear upon him.

Thorbjorn said: "This is a big man. I am no good at judging men if that is not Grettir the son of Asmund. No doubt he thinks that he has sufficient business with us. We will meet him boldly and show him no signs of fear. We must act with a plan. I will go on ahead towards him and see how we get on together, for I will trust myself against any man if I can meet him alone. Do you go round and get behind him; take your axe with both hands and strike him between the shoulders. You need not fear that he will hurt you, for his back will be turned towards you."

Neither of them had a helmet. Grettir went along the marsh and when he was within range launched his spear at Thorbjorn. The head was not so firm as he had intended it to be, so it got loose in its flight and fell off on to the ground. Thorbjorn took his shield, held it before him, drew his sword and turned against Grettir directly he recognised him. Grettir drew his sword, and, turning round a little, saw the boy behind him; so he kept continually on the move. When he saw that the boy was within reach he raised his sword aloft and struck Arnor's head with the back of it such a blow that the skull broke and he died. Then Thorbjorn rushed upon Grettir and struck at him, but he parried it with the buckler in his left hand and struck with his sword a blow which severed Thorbjorn's shield in two and went into his head, reaching the brain. Thorbjorn fell dead. Grettir gave him no more wounds; he searched for the spear-head but could not find it. He got on to his horse, rode to Reykir and proclaimed the slaying.

The woman who was out in the field with them witnessed the battle. She ran home terrified and told the news that Thorbjorn and his son were killed. The people at home were much taken aback, for no one was aware of Grettir's arrival. They sent to the next homestead for men, who came in plenty and carried the body to the church. The blood-feud then fell to Thorodd Drapustuf, who at once called out his men.

Grettir rode home to Bjarg and told his mother what had happened.

She was very glad and said he had now shown his kinship to the Vatnsdal race. "And yet," she said, "this is the root and the beginning of your outlawry; for certain I know that your dwelling here will not be for long by reason of Thorbjorn's kinsmen, and now they may know that they have the means of annoying you."

Grettir then spoke a verse:

Asdis said it was true: "but I know not what counsel you now mean to take."

Grettir said he meant now to visit his friends and kinsmen in the western regions, and that she should have no unpleasantness on his account. Then he made ready to go, and parted with much affection from his mother. First he went to Melar in Hrutafjord and recounted to his brother-in-law Gamli all his adventure with Thorbjorn. Gamli begged him to betake himself away from Hrutafjord while the kinsmen of Thorbjorn were abroad with their men, and said they would support him in the suit about Atli's slaying to the best of their power. Then Grettir rode to the West across the Laxardal Heath and did not stop before he reached Ljarskogar, where he stayed some time in the autumn with Thorsteinn Kuggason.