NSW Assistant Police Commissioner Mark Murdoch's son is under investigation for allegedly repeatedly punching a spectator during an arrest at the Sydney Cricket Ground.

Video footage of the incident, aired by the Seven Network yesterday, showed the 39-year-old male spectator being punched at least five times by a uniformed policeman during a Big Bash match on Wednesday.

It emerged today that Mr Murdoch's son was shown in the footage, with Macquarie Radio Network reporting he was the officer punching the spectator.

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Police later said: "We can confirm that the relative is Mr Murdoch's son and that he is the officer depicted in the vision."