YOBS caused terror on a bus from Halifax to Huddersfield.
Passengers were showered in glass after a missile shot through the bus windows.
About a dozen commuters were travelling when the object – thought to have been fired from a pellet gun or sling shot – smashed through one side pane before crashing out another.
The bus was the 501 service travelling from Halifax to Huddersfield.
It was attacked as it neared the foot of Salterhebble Hill, Salterhebble, Halifax, at 8.30pm on Tuesday.
Police said two youths were seen running from the scene.
The bus stopped further down the hill and passengers were transferred to another vehicle.
Bus operator First said the firm would be working with police to catch the culprits.
Police urged anyone with information about the attack to ring them on 0845 6060606.