Keiran Clare told a jury that Commonwealth Games hopeful Craig Stewart injured him after they clashed during a Halloween pub crawl in 2012.
Mr Clare, 22, told Livingston Sheriff Court that he was out with pals dressed as disciples of Jesus the night of the alleged attack.
He said he heard Stewart, 23, shout abuse at him and his nine friends as they passed the Twig nightclub in Bathgate, West Lothian.
He told the jury: "I just walked away."
Moments later, he said, Stewart approached him and asked where he could go to the toilet, saying he was a stranger to the area.
After a brief conversation, he claimed Stewart said: "Do you want to go then?" offering a fight. He said: "I went to turn away and he lunged at me."
During the ensuing struggle Mr Clare said Stewart got on top and bit him on the chest before one of the "disciples" kneed him off. He said the accused left, then returned to attack again.
He claimed Stewart threw 15 to 20 kicks and punches at him as he curled into a ball in a bid to protect himself.
He said Stewart then started "sinking his teeth into my back". The jury was shown pictures of four bite marks.
Mr Clare went on: "He flipped me over and just sat on top of me. He leaned to the side of my head and took a bite out of my ear.
"He was just down the side of my head chewing away."
He identified Stewart as his attacker.
Stewart, from Harthill, West Lothian, denies biting Mr Clare to his injury in Cochrane Street, Bathgate, on October 27, 2012. He and co-accused Benjamin Dahle, 21, of Blackridge, West Lothian, also deny repeatedly punching and kicking Mr Clare to his severe injury.
The trial continues.