The incident took place at around 8pm on Wednesday, May 9.
Mandy Parker, general manager of Ponds Forge International Sports Centre, said: “We are aware an incident took place in the café area at Ponds Forge on the evening of May 9, which wasn’t witnessed by any members of our staff.
“Whilst dealing with the situation the person in question ran from the sports centre and, despite searches both inside and outside the immediate vicinity of the venue, couldn’t be located.
“We have informed the police and gathered together CCTV footage taken during the time of the incident.
Rivelin Valley Road Sheffield: Body found after police search of Rivelin Valley
Hosepipe ban: Reservoir near Sheffield less than 15 per cent full as photos show how water levels have plunged
Sheffield weather: Met Office issues thunderstorm warning as heatwave set to end with heavy rain and lightning
High Green assault: Sheffield bus driver punched on his break leaving him with facial injuries
Rotherham missing boy: 13-year-old missing for 10 days as police make appeal
“I’d like to reassure our customers that this kind of incident is exceptionally rare at Ponds Forge and that my team dealt with it in a professional manner at the minimum disruption to our customers.”
Anyone with any information should call police on 101.