Police were transporting a man detained under the Mental Health Act to the hospital at about 4pm today whren the incident happened.
In a statement, a force spokesperson said: “While awaiting treatment, the man assaulted one of the police officers accompanying him.
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“Additional resources were dispatched to the scene to prevent any further offences, provide officer safety and to provide reassurance.
“The man was moved to a separate location to receive treatment.
“The officer has received minor injuries, but remained on duty. There was no threat to the wider community.”
Pictures emerged showing about five police cars at the hospital earlier.
Initial reports suggested that a man with a gun was at the scene, however this was ruled out quickly by both police and the hospital’s trust.
A hospital spokesperson said: “Earlier today, colleagues at Doncaster Royal Infirmary’s Emergency Department called the police to assist with a disruptive patient.
“The issue was dealt with quickly and no-one was harmed during the incident.
“We would like to thank visitors who were present at the time for their cooperation, our staff for their calm and quick response and South Yorkshire Police for their assistance.”