Probation officer Allan Robertson, 48, of Pontypridd, throttled Michael Bitti then punched him in the head.
He wrongly believed Mr Bitti, 42, was a rival Arsenal fan and started a row with him in a London pub toilet.
Robertson was sentenced to nine months, suspended for two years, at Blackfriars Crown Court.
He was also given a 12-month supervision order and banned from football matches for three years.
The married father-of-three had been found guilty of racially aggravated assault at a previous hearing.
Judge Deva Pillay said Robertson attacked insurance underwriter Mr Bitti without warning and without any provocation whatsoever.
"I have no doubt that you attacked him because you thought, wrongly as it turned out, he was an Arsenal supporter," said the judge.
"Having pushed him against the far wall of the toilet and having committed that initial assault you resumed that attack once one of your associates had entered the toilet and blocked the exit door.
"This was a cowardly attack upon an innocent man which resulted in injuries. So traumatised was Mr Bitti that he has not since attended an away game.
"I continue to fail to understand what madness possesses you and many others like you who normally live respectable and responsible lives to lose self control and responsibility, and descend into this kind of anarchical behaviour."
Robertson was also ordered to perform 100 hours unpaid work, and the judge added: "You know what that means, being a probation officer."
'Looking for trouble'
The court heard Robertson had resigned from his job and the case had left him facing financial ruin.
His wife and two of his grown-up daughters were in tears throughout the hearing.
The jury had been told Robertson was "charged up and looking for trouble" when he assaulted Mr Bitti at the Phibbers pub in Islington on 16 February last year.
Following the incident, Robertson went to the Emirates Stadium to watch Cardiff lose 4-0 to Arsenal in an FA Cup replay.
He was photographed at the stadium making obscene gestures and behaving like a thug, the jury was told.
Robertson had travelled to London on a coach of Cardiff fans, including his niece and sister.
Exploded in rage
He drank three cans of lager during the journey and went with a small group to the pub for a drink later in the afternoon.
Robertson was said to have taken offence when he heard Mr Bitti talking to his son about whether trouble would "kick off" in the pub.
He assumed Mr Bitti was a rival, asked him about his comments and exploded in rage.
The court was told Robertson swore and racially abused Mr Bitti for being English, and attacked him in front of his teenage son.
Mr Bitti was badly bruised on his hip and head.
Robertson, who had worked for the probation service for 17 years, said he only pushed Mr Bitti out of his way because he had felt threatened, and denied he had uttered a racial slur.
BBC News
