An Italian who threw part of his go-kart at a rival during a world championship final, prompting 2009 Formula One champion Jenson Button to call for a life ban, apologised on Monday and said he was leaving the sport.
Coverage of the KZ final on Youtube showed 23-year-old Luca Corberi crashing out and then waiting by the side of the track for rival Paolo Ippolito before hurling his kart's bumper at him. Nobody was hit.
Footage posted on social media showed further fisticuffs after the race at the South Garda circuit in Lonato, northern Italy.
The Gazzetta dello Sport website said Corberi had posted an apology on Facebook, before deleting it.
"There are no excuses to explain why I did something so shameful," it quoted him saying.
"I have decided not to take part in any other motorsport competition for the rest of my life."
Button suggested on Twitter that the Italian deserved a life ban: "Luca Corberi just destroyed any chance he had at a racing career after his disgusting behaviour at the FIA World champs," said the Briton.
The governing FIA said it had launched an immediate investigation.
(Reporting by Alan Baldwin, editing by Christian Radnedge)
