A man shouted "I’ve shanked him, I got him" after stabbing a 38-year-old man in Dewsbury Moor.
The attack happened at around 8pm on Sunday when the victim was walking along Gledhill Terrace and was approached by two men.
The victim was punched in the face and a struggle broke out. He was then stabbed in his backside, police have told.
Both suspects fled the scene and the man was treated in hospital for a flesh wound.
Police arrested a 25-year-old man yesterday morning and he remains in custody.
Detectives are looking to trace a second man who is 5ft 6, of stocky build and wearing a black jacket and black jogging bottoms.
Det Insp Andy Parr, of Kirklees CID, said: “A 25-year-old man remains in police custody and we are seeking a second suspect.
“We would urge any witnesses to get in touch either on 101 or via Crimestoppers on 0800 555 111.”
In unrelated investigations, police would like to speak to the people pictured in the image gallery below. The people pictured in the images may be witnesses as well as suspects. If you recognise anyone, contact police on 101 quoting the reference number on the image caption.