A man was left with a fractured elbow after being pushed out a train at Herne Hill and onto the platform.
The victim needed surgery after the altercation with a fellow passenger turned physical.
The incident started on the 6.13pm service from London Victoria on Wednesday, June 5.
British Transport Police have now appealed for any witnesses to come forward. They are especially keen to hear from travellers who went to the victim’s aid as he was pushed out the train at Herne Hill station.
They say the suspect was black, with a medium build, in his late twenties or early thirties, spoke with a ‘London accent’ and was travelling with a woman.
Anyone with information should call officers on 0800 50 40 50 or text 61016.