Former boxing world champion Joe Cordina was acting on 'instinct' when he punched another man outside a petrol station, a court heard.
The two-time IBF super-featherweight champion, 34, punched Jamie O'Brien, 33, when an altercation between the pair broke out at a Texaco garage in Pentwyn, Cardiff, in February, Cardiff Magistrates' Court heard.
The court was told Cordina had been filling up his Land Rover before he approached O'Brien, who had been sitting on the pavement near the exit.
CCTV footage played to the court showed O'Brien proceeding to push Cordina using his shoulder, before Cordina 'punched him with sufficient force to knock him to the ground'.
In footage shared on social media, a man dressed in a pink hoodie appears to barge into a second man who was exiting the Texaco store, seemingly to return to his vehicle.
The second man is then seen taking a fighting stance and raining several punches on his opponent, who then drops to the floor.
The pair were arrested after the flare-up.
Cordina previously pleaded not guilty to two charges of assault by beating against O'Brien.
Former boxing world champion Joe Cordina, 34, (right) outside Cardiff Magistrates' Court, where he is charged of assault by beating
The two-time IBF super-featherweight champion punched Jamie O'Brien, 33, when an altercation between the pair broke out at a Texaco garage in Pentwyn, Cardiff, in February, Cardiff Magistrates' Court heard
O'Brien pleaded guilty to assaulting Cordina and was ordered to pay £85 court costs and pay a mandatory surcharge of £26.
Alex Orndal, prosecuting, said: 'It is the Crown case that Cordina has initiated the confrontation.
'Mr O'Brien had his hands in his pocket and did not present a threat.'
The court heard the two men continued to 'remonstrate' with one another and exchange blows.
Mr Orndal said: 'There comes a point at which Mr O'Brien is entirely restrained by one of the other persons present.
'It is the Crown case that Mr O'Brien no longer presents a threat to Mr Cordina.
'Mr Cordina moved around the person restraining Mr O'Brien and threw a further punch at him – this is the subject of the second charge.
'Mr Cordina's actions went beyond lawful self-defence,' he said.
Mr Orndal said Cordina's defence was that he had struck O'Brien because he 'felt threatened'.
He said: 'He then said he punched him in the later part of the incident out of instinct, due to Mr O'Brien's actions.'
Video footage appears to show the boxer punching a man outside a petrol station
Video footage showed the two men in a brawl outside the petrol station
The footage, shared online, a man dressed in a pink hoodie appears to barge into a second man who was exiting the Texaco store, seemingly to return to his vehicle
The court heard police began to investigate the incident after footage of the altercation outside Pentwyn Service Station in February was circulated online.
The trial continues.
Cordina was due to fight for the WBO lightweight title in the United States on July 4 before his US visa was refused.
The Cardiff fighter, who has a 19-1 record including nine knockouts, revealed in an Instagram story in June that his application for a US visa had been rejected, triggering the collapse of a July 4 bout against Abdullah Mason in Cleveland.
In a video, he said: 'Just to let everyone know that I'm not going to fight. There's no injuries, I've had a great camp and I was meant to fly over this week.
'A couple of days back, I went to the US embassy in London and they basically denied me a visa. I tried to explain certain things and I had all the paperwork to back it up and they wasn't having it.
'They just basically told me 'you ain't getting in'. It's out of my hands and I'm absolutely gutted because it was my chance to become a three-time, two-weight world champion.'
Cordina represented Wales at the 2014 Commonwealth Games where he took home bronze, before going on to win a gold medal at the 2015 European Championships.
He also represented Team GB at the 2016 Olympics.