A gunman targeted a passenger train as it passed through Doncaster, putting lives at risk.
The pellet from an air gun struck one of the carriages as it went past Hatfield Colliery, shattering one of the windows.
British Transport Police (BTP) is appealing for information from the public after the incident
The attack happened at around 2.10pm on Sunday, May 31, as the Northern Rail service from Scarborough to Sheffield passed through the colliery in Stainforth.
Investigating officer PC Fran Hewlett said: “A passenger travelling on the service heard the crack as the pellet hit and smashed the window of the rear carriage and alerted staff.
“This was an extremely serious and reckless act which endangered the lives of passengers and the driver.
“It is vital we find those responsible and I would urge anyone with information to contact us immediately.”
Anyone with information is asked to contact British Transport Police on 0800 40 50 40, or text 61016, quoting reference PSUB/B7 of 17/06/2015. Information can also be passed anonymously to the independent charity Crimestoppers on 0800 555 111.