SINGAPORE - A relief teacher going through marital problems took them out on a nine-year-old autistic pupil, a court heard, by throwing a volleyball at his head and threatening to put him in a cage during a physical education (PE) class.

The 33-year-old man, who cannot be named to protect the victim's identity, also locked the boy in an equipment room with the lights and fan switched off.

He was sentenced to three months' jail and fined $3,000 by a district judge on Monday (Oct 8), having previously pleaded guilty to one charge each of child abuse and wrongful confinement of the boy, who is now 10.

The first incident took place during a PE lesson on March 6 last year, when the boy - who also has attention deficit hyperactivity disorder (ADHD) - had been pacing back and forth in front of his classmates while the teacher addressed the class.

The man threw a volleyball at the pupil's head three times in front of the group.

He later lifted the cover of a metal cage used to store equipment and threatened to put the boy inside it - even asking his classmates if they wanted to see him caged.

When the boy did not participate in a class activity, he grabbed the boy forcibly and took him to a PE equipment room where he scolded him.

Two days later, in another lesson, the teacher locked him in the equipment room with the lights and fan switched off for around a minute and a half.

When recounting this incident to an Institute of Mental Health consultant later that year, the boy "was very angry, screamed and hyperventilated", according to court papers.

Five months after the incidents, the boy was still affected by the incidents and dreamt that the man might do it again.

The boy's father reported the incidents to the police in April that year.

The school has since terminated the teacher's employment. The man later said that he could have committed the offences because he was frustrated by marital issues.

In her submissions, Deputy Public Prosecutor Kelly Ho called for the man to be jailed for at least three months for child abuse, and at least six weeks for wrongful confinement.

But defence counsel S. Balamurugan urged for the teacher to be fined, saying that his marriage had been deteriorating since August 2016, and he was "distracted and worried at work".

He added that the man was a passionate teacher, who is generally of good character, adding: "There were no complaints from other students that my client has acted as a bully."

District judge Kenneth Yap, however, said that victim is a pupil with special needs, whose "emotional scars are more serious".

In addition, the man's acts set a "very bad example to the victim's classmates," said the judge.

The man will start his jail term on Tuesday.