Two men have been charged with assault after an alleged coward punch attack during a junior rugby sevens grand final on Sunday, in which a referee was knocked unconscious.

It's alleged that after the under 14s game at Southwell Park in Lyneham, in Canberra's north, an 18-year-old man from Fairfield, NSW, entered the field and assaulted one referee.

The man's 42-year-old father, also from Fairfield, then allegedly "coward punched the second referee from behind" as he was helping the first referee, knocking him unconscious.

He was transported to hospital by paramedics.

Police say they spoke to witnesses who directed them to the 18-year-old man, who attempted to leave before being arrested and taken into custody.

Later that night, the father was arrested and taken to the watch house, whe

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