Fireworks were thrown at a blind woman and her guide dog in a "shameful" attack.
A gang of three or four youths w were standing about 65ft (20m) from the victim, who is in her 50s, when the explosives were thrown.
Despite not being hit, she was left very distressed and her startled dog tried to flee the scene in Hyde Park, Leeds, West Yorkshire Police said.
The force said it was keen to speak to two women who came to victim's aid.
It has appealed for witnesses to the attack, on Moorland Road, near Woodhouse Moor, at about 20:00 GMT on Tuesday.
On Twitter, police said those involved should be "utterly ashamed" and "To the 2 good Samaritans that came to her aid, you should be proud."
To the individuals that aimed fireworks at a blind lady and her guide dog in @Hyde_Park_Leeds this evening, you should be utterly ashamed. To the 2 good Samaritans that came to her aid, you should be proud. Please RT and lets see if we can identify the witnesses and the suspects.— West Yorkshire Police - Leeds North West (@WYP_LeedsNW) October 30, 2018
Officers are also checking CCTV in the area.