Detectives have launched an investigation after a man was found collapsed with serious head injuries in Todmorden.
The 55-year-old, who was lying on the ground outside Pickles Court, was found by officers at about 10.50pm on Friday.
Police today said they have now launched an attempted murder investigation.
The victim was taken to Leeds General Infirmary after he was found, where he remains in a critical but stable condition.
A 28-year-old man was arrested on suspicion of attempted murder and has now been released under investigation, police said.
Detective Sergeant Ross Wadsworth, of West Yorkshire Police, said: “The victim has sustained a number of serious injuries before being found and I am certain that there will be someone who will have seen what took place, or who will have information about the incident.
“I am appealing to anyone who has any information about what happened to come forward. Enquiries are ongoing.”
Anyone with any information is asked to contact Calderdale CID via 101 quoting 13170526850. Information can also be passed anonymously and in confidence to the independent crime fighting charity Crimestoppers on 0800 555 111.