Armed robbers threatened staff and stole money from the Rockdale Tennis Club on Thursday night.
St George police said two men confronted two employees at the Chapel Street club about 11.20pm when staff were closing up.
They said one man was armed with a handgun and the other man had a sledgehammer.
There were two customers in the club at the time.
The men took cash and ran from the building.
They were last seen leaving in a silver Audi station wagon, driven by a third person.
The men were described as wearing dark jumpers and pants and both had their faces covered.
St George Police urge anyone with information to call Crime Stoppers on 1800 333 000 or use the Crime Stoppers online reporting page: www1.police.nsw.gov.au