A 45-year-old woman was assaulted while walking her dog in Ripponden.
The victim was walking along Hanging Stones Lane with her dog when she was grabbed on the arm by a man.
The man pushed her and pulled her hair before making off.
It happened between 5.30pm and 6pm on the lane which runs through a wooded area and is used often by dog walkers, on Saturday, August 31.
Officers want to speak to a man aged in his 40s with natural blonde hair and acne scarring on his face in connection with the incident.
He was wearing black trousers and a blue and white thick striped t-shirt. He smelt of cigarette smoke.
Any witnesses to the incident are asked to contact the Upper Valley Neighbourhood Policing Team on 101.