A video posted on Twitter after Chicago's first World Series win in 108 years shows a man dressed in a Cleveland shirt punching and knocking out another man wearing a Cubs jersey.
The Cubs beat the Cleveland Indians 8-7 Wednesday in a thrilling series finale.
The video was posted by Chris Vallimont, a Pennsylvania native and a Cleveland Indians fan.
Vallimont told the Washington Post he watched the game from at a party outside Progressive Field when around 12:50 am he spotting the two men getting into an altercation.
“Naturally, I just looked over, and both men were getting very heated and started saying stuff they probably shouldn’t have,” he told the Post. “And then they both said, like, do you want to fight right now?”
That's when the man wearing a red "Cleveland against the world" shirt swung his right fist and punched the Cubs fan in the face.
The Cubs fan fell to the ground. Vallimont said he stayed they way until paramedics and police reached him.
The Cubs fan, identified by Cleveland police as Alan Anderson, 36, initially refused treatment, but was then transported to a local hospital with a cut to his mouth and a head injury.
The name of the man who punched Anderson remains unknown, police said. Anderson told police he did not want to file a report. Investigators have reached out to Anderson but have not heard back as of yet.
A request for additional information from Vallimont was not immediately returned.