The victim, aged 21, was walking along a footpath between Grosvenor Road and Standiforth Place, in Dalton, at about 3pm yesterday (Friday) when he saw a youth leaning against the fence.
The youth asked for the time and as the victim got his phone out to check he produced a knife.
Fearing for his safety the victim punched the suspect, but then felt something on his leg and saw blood.
The suspect fled towards Grosvenor Road and the victim later was later treated at hospital and had two stitches to a cut. He dropped his phone during the incident and it has not yet been recovered.
The suspect is described as white, aged about 15, 5ft 9ins tall and stocky. He was wearing a black, waist-length, padded coat with a hood and light grey jogging bottoms.
Det Con Carla Senior, of Kirklees District CID, said: “This was clearly a very distressing incident for the victim to be attacked with a knife in this way and we urgently need to identify the person responsible.
“We would like to hear from anyone who saw a youth fitting this description in the area around the time of the incident or anyone who has any information that could assist the investigation.”
Anyone with information is asked to contact DC 4321 Senior at Huddersfield Police Station via 101 quoting crime number 13160412757 or call Crimestoppers anonymously on 0800 555 111.