When a top rugby star retires and wants to stay involved in the sport, they usually play club rugby or become a coach.

But not former French No8 Sebastien Chabal.

Chabal caught fans at the Hong Kong Sevens by surprise when he took to the field dressed as a caveman while singing 'I'm Gonna Be (500 Miles)' by Scottish band The Proclaimers.

Commentator Sean Maloney couldn't hold back his laughter as Chabal, who was at the heart of France's epic 20-18 win over the All Blacks at the 2007 Rugby World Cup, belted out the song alongside three other men also dressed in caveman outfits.

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"Things I never thought I'd see on a Friday afternoon in Hong Kong," he said. "I've never seen anything like this on a rugby field.

"Only in Hong Kong. That's is the best. I've seen it all."

Even fans couldn't get enough of the video on Twitter, which has already been viewed more than 176,000 times on the World Rugby Sevens page.

"This is fantastic!!!" one fan wrote, while another hailed it as "pure perfection".

Meanwhile, New Zealand won their opening game at the Hong Kong Sevens over Australia with two more pool games against Kenya and Fiji tonight.