The 15-year-old allegedly attacked a 17-year-old in a car park on Morehead Road, Redfern, in southern Sydney about 6pm on Wednesday.
Police were called to the nearby Redfern Oval, where they found the older boy with his hand barely attached.Â
He was allegedly attacked with a knife, police said.
The victim was taken to hospital, where he was in a stable condition on Thursday morning.
AAP on Thursday found what appeared to be dried blood splattered on the ground of the car park.
The younger boy was arrested about midnight when officers stopped a vehicle in traffic near the scene.
He remained in a cell overnight after he was charged with wounding a person with intent to cause grievous bodily harm, and breach of bail.
The boy did not say a word when he faced Surry Hills Children's Court on Thursday morning.
"It's a serious children's offence," Judge Keisha Hopgood told him.
No application for bail was made.
The boy was remanded in custody until his next court appearance on October 6.
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