An Oregon father is suing his son's school for over half a million dollars over injuries the boy allegedly suffered at the hands of a bully. 

Gregory Bang filed a $600,000 lawsuit against the Eugene School District, four of its students, and their parents for the May 27 incident at Cal Young Middle School, the RegisterGuard reports. 

According to papers filed in Lane County Circuit Court, Bang alleges that the children were unsupervised during a lunch period, and the four students beat up his son on a playing field. 

Allegedly, the boy and one of the students began fighting after a football was intentionally thrown at Bang's son's head. After the pair separated, a second student tackled the boy, and began punching him

The other three boys then joined in the beating, even choking the outnumbered student. The boy suffered bruising to his head, neck, and torso, in addition to alleged psychological damage. 

The lawsuit said the assailants "had a history of intimidating, harassing and assaulting younger students," and school officials failed in their responsibility to protect Bang's son. 

A week after the attack, Principal Kim Watry sent a letter to parents informing then of "a troubling incident at school," and described the assault as "extremely unusual at our school, and it is absolutely not acceptable."

The four boys signed "formal accountability agreements" to avoid criminal charges, and the school increased lunch supervision immediately after the incident. 

District spokeswoman Kerry Delf declined to comment, and neither Bang nor his attorney, Kevin Brague responded to media requests.