 The train affected was the 1417 BST from Victoria to Southampton |
A passenger suffered cuts from flying glass after a vandal hurled a rock through the window of a moving train. An ambulance was called to meet the South Central service at Southampton Central after the incident, which happened at 1730 BST on Wednesday.
A group of youths were spotted on the Keepers Crossing walkway above the track in Sholing, Southampton, before the rock was thrown, police say.
The man was treated at the station and did not need hospital treatment.
'Very serious'
The 22-year-old was talking on his mobile phone when he was injured, a spokesman for British Transport Police said.
"We hear of things being thrown at trains, but very rarely do passengers get hurt," he told BBC News Online.
Another object was thrown at a second train at around the same time, he added.
He said they were taking the incident very seriously.