The spray left the victim with soreness to his eyes and burning to his face
A man was attacked with a pepper spray and then threatened with a knife after he scolded youths for dropping litter.
The 38-year-old man's eyes were left burning after being squirted with the substance in Lulworth Drive, Plymouth.
He cleared his vision sufficiently to drive off in his car as a youth brandished a knife at him. He was later treated by ambulance staff.
Devon and Cornwall Police said a 14-year-old boy arrested in connection with the incident had been bailed.
Pepper spray is illegal under the Firearms Act but can be bought for as little as 10 euros over the internet and mailed to the UK.
Studies have shown such sprays can cause blistering, swelling and skin inflammation.
Devon and Cornwall Police no longer use the more powerful CS spray when tackling violent offenders because of safety concerns.
They now instead use Captor spray which forces a person's eyes to close and works for up to 40 minutes. It has no lasting side effects and is less likely to affect those not targeted by it.
Anyone who witnessed the attack at about 1800 BST on Monday outside Widewell Primary School is asked to contact police or Crimestoppers.