A paramedic needed hospital treatment after she was assaulted while attending to a road crash victim.
The woman, who has not been named, was treating a driver who had been involved in a collision in Leicester when she was attacked.
She suffered significant injuries and was taken to hospital for treatment.
The assault took place after emergency services were called to a crash involving a silver Mercedes and a black BMW just before 11pm last Thursday in Catherine Street.
Leicestershire Police said a 40-year-old man was arrested on suspicion of assault, being drunk in charge of a vehicle and failing to stop at the scene of a road traffic collision. He has since been released on bail, pending further enquiries.
The paramedic, who is believed to be in her 20s, has since been discharged from hospital.
Leicestershire Police are investigating the collision and the assault and are appealing for witnesses to contact them.
Detective Constable Sukhvinder Obhi said: "No one was seriously injured in the collision but whilst the paramedic was treating one of the drivers she was assaulted and received significant injuries.
"If you witnessed any part of the incident whether it was the collision itself, the events leading up to it or the subsequent assault on the paramedic then we need to speak to you."
Nick Arnold, from East Midlands Ambulance Service, said: "It's a sad reflection on society that some people who we are trying to help at incidents think it's alright to physically assault our staff and this incident is particularly distressing.
"Our paramedic colleague suffered significant injuries requiring hospital treatment. We continue to support her and are working closely with the police to ensure a successful outcome."