It is a challenge for sports leagues across the world - if play can only resume in empty stadiums, how can the atmosphere be improved?

However, not many clubs will be rushing to follow the example of FC Seoul.

The top-flight South Korean side has apologised after fans accused them of using sex dolls in the stands.

FC Seoul insisted they were "premium mannequins" rather than sex dolls - but did admit they came from a supplier that produces sex toys.

And some of the dolls were holding signs advertising x-rated websites - despite pornography being banned in South Korea.

The mannequins' manufacturer told the BBC they had apologised to FC Seoul. But they also reiterated that the dolls were merely "premium mannequins".

What happened at the match?

On Sunday, FC Seoul played their first home match of the K League season.

The ground was empty - one of many measures designed to prevent a Covid-19 outbreak.

So before the match, a company called Dalcom offered to fill some of the empty seats, and the club agreed.

In total, there were 30 mannequins - 28 of them female, and two of them male.

However, fans watching online noticed that some of the mannequins looked more like sex dolls - and some were advertising x-rated websites - leading to the club apologising on Instagram and Facebook.

Dalcom said the adverts came from a sex toy company who placed orders with Dalcom, and wanted to take pictures of the mannequins before the game.

"They were supposed to take all the logos down before the game started," Dalcom director Cho Young-june told the BBC. "But there were several hairbands and logos left to be caught by public eye."

FC Seoul official Lee Ji-hoon told the BBC it didn't do a background check on Dalcom, and didn't realise they worked in the sex industry.

Mr Lee admitted he thought the dolls looked "very human" - but said it didn't even enter his mind that they could be sex toys.

When did football resume in South Korea?

The 2020 K League season was supposed to begin in February but was delayed because of the virus outbreak.

But South Korea's success in fighting the virus allowed football to resume sooner than almost everywhere else.

And, when the season began on 8 May, the K League was one of the few places for sports fans to get their fix - leading to increased global attention.

The opening match - Jeonbuk Motors versus Suwon Bluewings - was even streamed live by the BBC.

As well as empty stands, handshakes are banned, and coaches have to wear facemasks.

"Excessive spitting or blowing of the nose is prohibited and players should refrain from close conversations," said a K League official before the first match.

Which other football leagues have resumed?

The Bundesliga in Germany resumed at the weekend, but, like South Korea, with no fans present.

The Premier League in England has a tentative return date of 12 June - but there is a "growing feeling" this will need to be pushed back.

Other leagues, such as France's Ligue 1, have cancelled their season entirely.