World Under-21 finalist Lewis Bridger, 18, and pals Matthew Dawes, 24, and Luke Cornelius, 18, attacked Sangem Kim after claiming he boasted about his martial arts skills.
Lewes Crown Court heard how the assault was sparked by Great Britain under-21 rider Bridger who told Mr Kim, "I don't like people like you."
Prosecutor Michael Warren told the court the attack happened at TJs nightclub in Eastbourne on December 12 at 2.30am.
He said, "All of a sudden a blow is struck to Mr Kim and all hell breaks loose.
"All three defendants then become involved in assaulting Mr Kim. He remembers the first punch and trying to put his hands out to try to push the male away.
"He then felt himself being hit several times from different directions. He eventually went down to the ground and could feel himself being punched several times.
"The bouncers tried to protect him but at any opportunity the defendants were still trying to strike him."
In interview Bridger admitted throwing a punch and told police he was "backing his mates up" during the brawl at the Terminus Road nightspot.
The court heard that Mr Kim, 28, suffered a sore jaw and elbow but was not seriously hurt and did not need hospital treatment.
Bridger, of Westville Road, Bexhill, Dawes, of Bidwell Avenue, Bexhill and Cornelius, of Meads Road, Eastbourne, admitted assault. A charge of racially-aggravated assault was dropped.
Philip Meredith, defending Bridger, told the court he rode in Poland, Sweden and Slovakia.
He said, "He has a very specialist occupation on which he has been focused since before he left school.
"He rarely drinks because in his trade it makes sense if he wants to be successful.
"If he's getting on a speedway bike he doesn't want to be under the influence of alcohol. This was an unfortunate phase during the closed season.
"The comment, 'I don't like people like you', was in no way a reference to his race or colour. It was simply his attitude but that doesn't excuse what happened."
The court heard that Dawes has previous convictions for common assault and Cornelius has two cautions for assault and shoplifting.
Defending the pair, Justin Rivett said, "This was clearly an ugly and unpleasant incident and one that neither of them are in the least bit proud of.
"They accept that no actions were taken by Mr Kim which justified their reaction."
Judge Charles Kemp ordered Bridger to pay a £1,500 fine and £500 compensation to his victim after watching CCTV footage of the attack.
He told him, "You have the most to lose in view of your chosen career because if I lock you up you would have to forfeit some of your time which is doubtless lucrative and important to you in the furtherance of your career."
Dawes, who threw the first punch, was given a six-month jail sentence suspended for two years. He was also ordered to do 100 hours' unpaid work and pay £300 compensation.
Cornelius, a trainee carpenter, was ordered to do 60 hours' unpaid work and pay £200 compensation.
Last season Bridger, a former British under-18 champion, raised his average points haul per meeting to over five-and-a-half and competed in the World Under-21 Championship.
He is regularly seen on Sky Sports riding for his home team Eastbourne Eagles at Arlington Stadium.