A video was circulated on social media which apparently showed the 15-year-old being kicked in the head and pushed into the Mirror Pool water feature in front of Bradford City Hall.
In the footage, which features a large number of youths, a member of council staff can be seen near the group of teenagers - but he does not appear to try and stop the attack.
Many social media users questioned why the man, whom they believed to be a security guard, had not intervened in the brawl.
The council have now conformed that the man is a City Park custodian who is tasked with maintenance of the site. The custodians are not permitted to become involved in violent altercations and do not have a security role.
Coun Abdul Jabar said:
“This footage shows a very disturbing incident but fortunately events like this are rare in City Park.
“As soon as our City Park custodian saw the youths gathering he informed our CCTV team who called the police. He then approached the youths to tell them that the police were on their way.
“Our City Park custodians are not security guards, their role is to provide customer service, maintenance and cleaning. They are under strict instructions not to intervene in events such as this, but to call police who are the appropriate professionals to deal with such incidents.
“The employee, who behaved absolutely correctly, then also went to the aid to the injured youth. As a result of his actions the police were on the scene quickly to investigate and prevent further trouble.
“As this is now a criminal investigation we cannot say any more about it but we reiterate that City Park receives many thousands of visitors every year who enjoy themselves without any trouble whatsoever.”
West Yorkshire Police have arrested a 16-year-old boy on suspicion of assault. He was released on bail and enquiries are ongoing.