A 33-year-old man who admitted headbutting his girlfriend’s brother was fined $500 at Magistrates’ Court today.Demetrius Byrd, of Devonshire, pleaded guilty to unlawfully assaulting Roderick Cox and causing him bodily harm on July 13.The Crown offered no evidence on two charges of unlawful assault and using threatening words, which Byrd denied.Prosecutor Cindy Clarke told the court that Byrd entered the back yard of the Cox family’s Devonshire home — where he and his girlfriend live — and proceeded to deliberately get in the way of Mr Cox and son Kaylen Cox, who were gardening.She said Byrd’s behaviour led to an altercation between him and Roderick Cox, with Byrd shouting: “Don’t touch my f****** stuff, you f****** p****. I will slap you and your son. I will slap you.”Ms Clarke said Byrd headbutted Roderick Cox and kicked Kaylen Cox in the face.The defendant then picked up a metal chair, raised it to shoulder height and threw it at the father and son. Roderick Cox was taken to hospital to receive treatment for a cut above his right eye, while Byrd escaped on foot.Byrd told Senior Magistrate Archibald Warner he acted in self-defence, claiming Roderick and Kaylen Cox were “karate experts” who got “in his face”.“I’ve never headbutted someone before,” he said, adding that he was recovering from pneumonia and “wasn’t there to fight”.Mr Warner told him headbutting someone was excessive and did not constitute self-defence. He warned Byrd to “stay away” from his girlfriend’s family.