A New Zealand rugby coach has admitted attacking his 11-year-old son after blaming him for the boy's team losing a match.

Alexandra District Court was told on Wednesday that the man returned home drunk last month, verbally abused his son, grabbed him around the throat and later headbutted him, The Otago Daily Times reported.

"The boy's team had lost its game and he blamed his son for the team losing," Sergeant Ian Collision said.

The boy's mother intervened and he was not injured but was "extremely frightened".

Judge Stephen O'Driscoll convicted the man of assault and remanded him on bail to reappear on September 23 for sentencing.

He said the pre-sentencing report was to include a drug and alcohol assessment.

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