A woman suffered serious leg injuries and her friend was also attacked after being set upon by a woman draped in a Rangers flag at a train station.
Detectives said a young woman was assaulted on Saturday at around 7.30pm at Coatbridge Sunnyside station in North Lanarkshire, suffering severe injuries to her leg.
She is being treated in hospital.
Her friend, who rushed to her aid, was also attacked by the same suspect, who is described as a white female aged between 17 and 20, British Transport Police (BTP) said.
The suspect is also heavily built, with dark hair, and she was wearing black trousers with a Rangers flag around her neck.
The attacker was in the company of another female.
Several potential witnesses are believed to have been at the station at the time.
Anyone with information can contact BTP by texting 61016 or calling 0800 40 50 40, quoting reference 2100034030.
Alternatively, Crimestoppers can be contacted anonymously on 0800 555 111.
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