A train manager was allegedly assaulted after two men didn't pay for tickets and locked themselves in the toilet.
British Transport Police (BTP) said two men are reported to have boarded the train between Cardiff and Bridgend.
The two men are reported to have boarded the train without a ticket and locked themselves in the toilet.
A BTP spokesperson said: "When the train arrived at Bridgend they exited, and on their way off the train one of the men grabbed hold of the train manager and pushed him."
They then ran across the railway lines on their way out the station.
The incident happened between 12.30pm and 1.20pm on Wednesday September 25. Officers have now released CCTV images and are appealing for information.
Anyone with information is asked to contact BTP by texting 61016 or by calling 0800 40 50 40 and quoting reference number 1900082835.
Alternatively contact Crimestoppers anonymously by calling 0800 555 111.
