Police are appealing for information after the crash today.
A blue Lexmoto Assault motorbike was travelling on the A645 Knottingley Road, in the direction of Knottingley at around 12.30pm, when the rider came off the bike and hit what West Yorkshire Police has called "street furniture".
Police said the rider, a 39-year-old man, was seriously injured. He remained in hospital tonight.
Anyone who saw the crash or the vehicle being driven beforehand is asked to contact police.
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Officers would also like to hear from anyone who has 'dash-cam' footage.
Call police on 101 or via the West Yorkshire Police online chat facility, quoting log number 880 of September 27.