An off-duty police officer suffered head injuries when he was assaulted by four men.
Avon and Somerset Police are appealing for witnesses after the officer stepped in when he saw somebody being attacked.
The incident happened outside the theatre between 8.20pm and 8.45pm on Sunday, August 29.
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Avon and Somerset Police said in a statement: "We’re asking witnesses to come forward after an off-duty police officer suffered injuries while assisting the victim of an assault in Bristol city centre.
"A male offender pushed a man off his bike in an unprovoked assault, leaving the victim with leg injuries. The offender was not known to the victim.
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The officer, who was off-duty at the time of the incident, stopped to assist the victim and was assaulted by the offender and three other unknown men.
"He suffered head injuries and was treated in hospital," police said.
A man in his 30s was arrested in connection with the incident and has been released under investigation.
Police would like to hear from anyone who witnessed what happened or can help them identify those involved.
Anybody who can help is asked to call 101 quoting crime reference 5221199986.
