Hampshire police said the male dog walker had been asked to leave as his German Shepherd was chasing horses.
It happened in a field on Woodcroft Lane, Waterlooville, yesterday between 5.50pm and 6.20pm.
The dog owner, who was white, about 5ft 6in tall, stocky, in his late 20s to early 30s and with short dark hair, left the field towards the Wecock estate. He was with a woman.
PC Lee Smith said: ‘We would like to hear from anyone who thinks they saw this man walking his dog in the area at the time of this incident.’
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Call PC Smith on 101, quoting 44160175897.
It comes after the force revealed several separate arrests were made across the county in a week of action against knife crime.
Operation Sceptre, which started on April 25, aimed to take knives off the street.
Chief Inspector Claire Taylor said: ‘Operation Sceptre is an anti-knife crime initiative which was started by the Metropolitan Police.
‘Hampshire Constabulary is one of the forces across the UK which has adopted the campaign and brand.
‘Fortunately gang-related knife crime is very rare in Hampshire and on the Isle of Wight, therefore our focus is on four areas: tackling and disrupting the supply of knives, targeting those who carry and use knives, preventing people from getting involved in knife crime and increasing prosecution.
‘We are also working with partner agencies, young people, and retailers, through education and intervention activities as part of Operation Sceptre.’