An alleged football hooligan only head-butted a rival fan through fear of being hit, a court has heard.
Crystal Palace fan Clive Taylor told Southwark Crown Court he was trying to avoid trouble during the brawl at Sydenham rail station last September.
The prosecution alleges a gang of Palace fans ambushed the train to stop Charlton Athletic fans escaping.
Mr Taylor, 35, of Marion Road, Thornton Heath, south London, is one of six men who deny violent disorder.
CCTV footage of the chaos was shown to the jury in the trial on Wednesday.
The clashes erupted when a group of more than 30 Palace fans boarded a train full of Charlton supporters ahead of a local derby between the south London rivals.
Mr Taylor said he could hear the rival fans chanting and banging on the windows as the train arrived, but dismissed it as "banter".
He said that once he was on the train he turned around and "saw the commotion".
He told the court: "I saw beer getting thrown and pushing and shoving."
"I was just trying to get out of the way," he added.
He said a Charlton supporter accused him of throwing a bottle, and in fear of getting hit he head-butted him.
Alan Kent, prosecuting, asked Mr Taylor why he had chosen to go to Sydenham before the match, when trains carrying rival supporters passed through that station.
But Mr Taylor said it was convenient, and that it was a coincidence that the group of Crystal Palace fans had ended up in the same place.
The other defendants are Carl Thomas, 40, of Foxley Road, Thornton Heath, south London; Mark Kirby, 37, of Ham Road, Worthing, West Sussex; Darren Bush, 39, of Woodside Green, Croydon, south London; and Ashley White, 21, of Higher Drive, Purley, Surrey.
The trial continues.