A HUDDERSFIELD boy of 14 slashed a 16-year-old's head with a carpet knife, a court heard.
Ryan Hanson was made the subject of a one-year detention and training order.
He is already in detention after being sentenced to six months for house burglary and possessing a knife in a public place.
Judge Robert Bartfield, sitting at Bradford Crown Court, told him his new sentence would begin at the end of his current one.
Hanson, of Wood Terrace, Primrose Hill, was originally charged with wounding with intent to cause grievous bodily harm following the slashing in September.
But on Wednesday the prosecution accepted his guilty plea to the lesser charge of unlawful wounding.
Prosecutor Christopher Attwooll said the victim had been sitting outside an opticians in Waterloo when Hanson approached him.
Mr Attwooll said there had been a previous fight between the two and Hanson asked him for a fight again.
He said the 16-year-old tried to throw a punch and the next thing he remembered was being slashed and blood running down the back of his head.
The teenager had 13 stitches put in the head at Huddersfield Royal Infirmary.
Hanson said he had bought some knife blades to cut carpet and he told police that one was in his hand when he punched the 16-year-old.
Hanson's barrister, Simon Myers, said his client realised that such an offence deserved a custodial sentence and he was sorry for what had happened.
Judge Bartfield told Hanson he had picked a fight with the teenager - then instead of using his fists he had used a knife.
"It could have been very much worse. You could have got the front of his head, you could have got his eyes or something like that," said Judge Bartfield.
"As it is the slash was bad enough.
"Thirteen stitches after you sliced open the back of his head with a Stanley knife."
The judge said courts had to send out the message that substantial prison sentences would follow for people who used knives.