Hafþór began his athletic career as a basketball player. At 2.06 m (6 ft 9 in), he started his senior team career with Division I club Breiðablik in 2004, playing as a center. In 2005 he joined FSu Selfoss, also in the Icelandic Division I. After 10 games it was discovered that he had been playing with a broken bone in his ankle and would require surgery. After recovering from surgery, Hafþór moved to Úrvalsdeild powerhouse KR in 2006. He missed most of the 2006–2007 season after a screw in his ankle shattered and had to be fixed by another surgery.
Seasons
For the 2007–2008 season, he moved back to play for FSu Selfoss. He averaged 6.7 points per game, helping the team achieve promotion to the Úrvalsdeild, but the troublesome ankle forced him to retire from basketball after the season, at the age of 20.
Between 2004 and 2006 Hafþór played 32 games for the Icelandic junior national basketball teams. In 2006 he played 8 games with Iceland's U-18 national team in Division A of the U18 European Championship.
