Police are appealing for information after a 17-year-old boy and his girlfriend were approached by a man at the top of a ginnel along Clover Road near to the Gillbrands estate in Chorley.
The man shouted abuse at the boy before swinging at him with a knife.
The victim managed to block him with his arm and he fled on foot up Lidgate Road at around 8pm on Thursday January 2.
The man is described as being between 20 to 25, more than 6ft and skinny. He wore a dark hooded top and dark tracksuit bottoms and spoke with a local accent.
PC Steve Benko from Chorley Police said: “Fortunately the victim managed to defend himself and was unhurt.
I would reassure people incidents of this nature are rare in Chorley but I’d appeal to anyone who may have any information about the identity of this man to contact us.
“He is described as being under the influence of drink and drugs or suffering from a mental illness.” Call 101.