Officers were called to Riverside Walk in Thetford at 9.06pm on Tuesday following reports of an altercation. The man, who suffered head injuries, has since been discharged from hospital. Three teenage boys were arrested on suspicion of assault and remain in custody at Wymondham Police Investigation Centre for questioning. A spokesman for Norfolk Constabulary said: "Officers would like to hear from anyone who witnessed the incident or has any information about the identity of those involved. "Anyone with information can contact Norfolk Constabulary quoting reference 36/55837/26."