Britain's Mark Cavendish collides with South Korea's Park Sanghoon during the Olympic omnium points race, with the crash also bringing down Elia Viviani.
The Italian picked himself up to win the event, with Cavendish escaping punishment and claiming a silver medal.
Park suffered a mild concussion and was taken to hospital.
"It was my fault, I should have been looking where I was going a bit more," said the 31-year-old Cavendish, who finally succeeded in adding an Olympic medal to his long list of accolades.
The incident sparked a furious debate on social media, with former road pro Michael Rasmussen, a convicted drugs cheat, tweeting that Cavendish's manoeuvre was worse than doping and he should have been disqualified.
Sir Chris Hoy, a six-time Olympic champion who was trackside for BBC Sport, defended his former team-mate, insisting the incident was "not intentional".
Former British track cyclist Rob Hayles, who won team pursuit silver and a madison bronze at the 2004 Olympics, agreed.
"There is always drama when Mark Cavendish gets on a bike," said Hayles. "It was an odd move. He obviously didn't see the guy."
He added that Cavendish did not benefit from the crash because it allowed riders to rest. "He would've wanted a hard race," said Hayles.
Watch full coverage of the event here.
Available to UK users only