NSW Police and the NRL will investigate an ugly incident involving former NRL bad boy John Hopoate at Saturday night's Test match between Samoa and Tonga at Pirtek Stadium.

A seemingly intoxicated fan was ejected from the ground after Hopoate and a Tonga team sponsor along with his son had a beer thrown on them. The Daily Telegraph has revealed Hopoate was not the instigator.

A Tongan supporter began heckling Hopoate, who was an unofficial coaching consultant for Tonga, during the Pacific Test.

After copping abuse for several minutes, Hopoate - who was sitting in the team dugout area - fired back, telling the fan to go away and sit down.

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It's understood the man then threw a beer that hit Hopoate, the team sponsor and his son, who were seated behind the former Manly and Wests Tigers star.

Police were forced to intervene and escorted the man from Pirtek Stadium.

A Tongan official on Sunday night said it was disappointing the incident took attention away from the spectacle of the Pacific Test, which was played before a passionate crowd of 15,225 fans.

There was no suggestion of any physical contact between the man and Hopoate. Police did arrive quickly to quell any potential drama.

The NRL confirmed on Sunday night it would launch an inquiry, more aimed though at crowd control rather than directly at Hopoate.

Pirtek Stadium officials are also expected to seek answers as to how the man was allowed to be so confrontational and intoxicated.

Hopoate was not commenting on Sunday.