The incident started at around 1.30am on Saturday August 5 on the northbound Jubilee Line platform at London Waterloo.
The fight broke out after a man became involved in a verbal altercation with four other men and during the journey another man joined in using his crutch as a weapon.
There was then a short break from the fight as he and the original man left the train at Swiss Cottage and waited for the next service, the other four men left the service at Finchley Road, with three of them rejoining the next service.
The fight began again and according to the police the two men were pinned to the floor and punched and kicked in the head.
Officers attended the incident as it spilled out onto the platform at Wembley Park station, arresting five people.
Investigating officer, detective constable Michael Baker, said: "I would like to speak to anyone who saw or heard the disorder on this train in the early hours of Saturday morning.
"We need as many accounts as possible from any potential witnesses in order to establish exactly what happened and the sequence of events.
"The man who was initially on his own was wearing very distinctive clothing which may jog people’s memories."
He is described by police as a black man with a Mohawk haircut and beard, at the time of the incident he was wearing a bright suit with a purple, brown and gold Moschino pattern over it.
Police say the man with the crutch who joined the fight was a black man wearing grey trousers and a blue jumper with white stripes.
The men in the other group are described as white men and around 18-years-old.
Three of the individuals involved required hospital treatment, but have since been discharged.
Detective constable Michael Baker added: "The people involved sustained injuries ranging from minor cuts and bruises to a fractured neck.
"It is essential that we establish the exact circumstances of this violent incident."
Anyone with information is asked to call British Transport Police on 0800 40 50 40 or text 61016, quoting reference 65 of 05/08/2017.
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