Pham Duy Duc, 42, of Huu Nghi Ward, Hoa Binh Province, is being held for "deliberately causing injury."

According to investigators, his son was playing with his first-grade classmates in the yard of Huu Nghi primary school in Hoa Binh on July 8 when a boy took his son’s hat and tossed it for other kids to play with.

The cap, apparently newly bought, then went missing.

Two days later Duc accosted the boy outside the school, pulled him into an alley and began to hit him. He did not stop until his wife and other people intervened, and the child was left bleeding from the nose and mouth.

The man was taken to the police station by passers-by.

Nguyen Thi Thinh, Duc’s wife, said her husband was a good father but had a bad temper.

The injured child is being treated at Hoa Binh General Hospital.

His mother, Ngo Thi Ngoc, said she and Duc’s families do not know each other aside from having their sons studying together.

She said the school has to be held accountable, but Duong Thi Thanh Huong, the school’s principal, said the attack took place outside the school before students had entered it and therefore the school has no responsibility.

Duc will be held by the police for four months as stipulated in the Criminal Code.

Deliberately causing injuries carries a jail term of six months to 15 years.