Police officers investigating stone attacks in Sheffield are urging victims to come forward to help with prosecutions.
South Yorkshire Police said large groups of youths congregating near to the U-Mix Centre in Lowfield have been throwing stones at passers-by.
The U-Mix Centre is a £2.5 million youth and community centre in Asline Road.
It offers 3G football pitches, a dance studio, recording studio, digital media suite, youth club and gym.
A spokesman for the Sheffield South West Local Policing Team said previous incidents of anti-social behaviour have been addressed.
"We are doing loads of work in the area to tackle the issue and have had a number of successful convictions," he said.
"We are also aware of those involved in the latest incidents, however what we need are witnesses and victims to come forward to build a stronger case.
"I am aware that often people are victim to this type of behaviour but don't report it for a variety of reasons. Clearly our case to the courts is much stronger if we have members of the public who are victims rather than police officers or CCTV evidence.
"We have in the past had cases where we have CCTV of youths throwing stones but no victim and then sometimes we struggle to take a case to court. So please everyone if you are victim of witness to this behaviour report it."
Anyone with information should call South Yorkshire Police on 101 or Crimestoppers on 0800 555111.