A teenager slashed a man across the face with a hunting knife in an unprovoked attack that was caught on CCTV.
Joseph Kaczorowski and five other young men went up to the unnamed 21-year-old as he walked with a friend in Northolt, west London, last year.
Film showed Kaczorowski swinging the knife and slashing the man across the face, leaving him with a 7cm deep cut across the cheek, Isleworth crown court heard.
Homebase worker Kaczorowski, now 18, of Ealing, West London, was sentenced to 18 months’ detention for unlawful wounding and nine months for possession of an offensive weapon.
The sentences will run concurrently.