North Yorkshire Police is appealing for witnesses and information about the assault inside The Pit in The Ginnel, Harrogate, in the early hours of Saturday.
Five men were arrested but have since been released under investigation while enquiries continue.
The fight involved numerous men around the age of 20 to 25, police said,
One man was seriously injured and taken to Leeds Royal Infirmary for treatment and is in a serious condition, officers added.
A North Yorkshire Police spokesperson said: "Five men were arrested on the evening in connection with the incident. They have been released under investigation while enquiries continue. We are requesting the public’s assistance to help establish the full circumstances surrounding the incident.
"In particular, we are appealing for information about details and description of the men involved."
Anyone with information that could assist the investigation should contact North Yorkshire Police on 101and ask for PC1982 Chris Dyson or DS1748 Andrew Palmer. People can also email [email protected] or [email protected]
Quote the North Yorkshire Police reference number 12180196889.