Thugs who were vandalising a railway shelter at a station in Leeds crossed the tracks to attack a passenger who had seen them from the other platform.
Three youths were banging the windows of the shelter at Cottingley station when they saw a 42-year-old man looking at them.
British Transport Police (BTP) said they hurled abuse at him and then jumped down onto the tracks to grab stones to throw at him.
They then climbed onto the platform to attack the man and only fled when a train arrived.
Det Con Jason Ridgeway, who is leading the investigation, said: “The victim, who was bleeding from his face and extremely shaken following the assault, was helped onto the train by passengers and taken to Leeds where he was given first aid by a BTP officer before being taken to hospital for treatment.
“He sustained a broken eye socket and cuts and bruises to his face as a result of the violent attack.
“This was a completely unprovoked assault on a man who was catching a train heading home. It’s vital that we trace the people involved.”
The incident happened at about 7.40pm on December 6.
The three youths were white. One had blond hair and was wearing a grey hooded top and black tracksuit bottoms. The other two were wearing dark clothing.
Anyone with information should contact BTP on 0800 405040, or text 61016, quoting reference PSUB/B5 of December 15.