Beckett, 54, is scheduled to go on trial in December on a felony charge of aggravated assault and battery. He maintains he was defending himself from Thomas at Henry Hudson's Pub in June 2007.
Beckett's attorney, Billy Bock said other witnesses at the bar have countered Thomas' version of what happened a year ago.
"Every bit of the investigation that's been done supports our side of things," Bock said.
The lawsuit was filed in Oklahoma County District Court.
According to Thomas' lawsuit, Beckett began heckling him after he walked into the bar wearing a Texas T-shirt. Thomas tried to ignore it, but decided to leave a short time later, the lawsuit stated.
Thomas said he was at the bar paying his tab when Beckett grabbed him and refused to let go until his scrotum was torn. The injury required more than 60 stitches, Thomas has said.
The lawsuit mentions "a possible connection to a local sports rivalry."
Beckett is accused of assault and battery and intentional infliction of emotion distress. The lawsuit also accuses Henry Hudson's of failing to intervene before the attack.
A manager at the bar declined comment on Thursday.