A man suffered a serious leg injury after an unprovoked attack at Brampton Manor Country Club in Chesterfield.
The assault happened following an afternoon charity boxing event held at the club on Old Road.
Shortly after 7pm, a 57-year-old man was punched several times in what police call a 'seemingly unprovoked attack' at the bar.
He suffered facial injuries and was later found to have a serious leg injury which required surgery.
The victim had been a spectator at the event and the suspect is believed to have also watched the boxing matches.
The suspect was with a friend and both men were wearing suits. They were ejected from the club after the assault.
The crime happened on Sunday, May 1, but police have only just released details to the media.
Anyone who can help police with their investigation should call Detective Constable Steve Topham on 101, quoting crime number 18896/16, or contact Crimestoppers on 0800 555 111.