A man was threatened by a group of teenagers on Radford Boulevard after he asked them to stop throwing snowballs at his car.
The incident happened at around 6.25pm on Sunday (December 10) and it is believed two of the youths had knives and the victim was also spat at.
No-one was seriously injured.
Detective Sergeant Kayne Rukas said: “Clearly this started as an act of anti-social behaviour and you would never expect youths to turn on you with a knife when you’re simply asking them to stop doing something that they shouldn’t be doing.
“However, you can never be too careful.
“If you do see someone doing something like this, please don’t intervene yourself – call us as soon as possible and let us deal with it.
“Luckily incidents like this are rare in Nottinghamshire but we do want to find those responsible so please get in touch with us if you can help.”
The attackers were four black males, aged between 15-16, all around 5ft 9ins to 5ft 10ins tall, clean shaven, of slim build and wearing dark clothing.
If you saw anything suspicious or have any information that could help, you are asked to contact the force on 101 quoting incident 726 of December 10.
You can also contact Crimestoppers anonymously on 0800 555 111.