Officers have released a CCTV image of two men they would like to speak to in connection with a train fight, which took place between Fishersgate and Portslade railway stations.
The incident occurred at around 4.30pm on the Littlehampton to Brighton service on Friday, March 9, police said.
Two men were fighting on the train and when a woman told them to stop, she was threatened by one of the men, a spokesman from the British Transport Police said.
Both men left the train at Portslade railway station, the spokesman said.
“Officers would like to speak to the men in these images as they may have information which could help the investigation,” the spokesman said.
Anyone with information, text British Transport Police on 61016 or call 0800 40 50 40 quoting 263 of 26 April.
Alternatively, contact Crimestoppers anonymously on 0800 555 111.