A terrified boy was forced to wade into water up to his neck after supposedly "grassing" on two bullies over a stolen motorcycle.
The 15-year-old was driven around eight miles to a village in East Yorkshire where he was assaulted and "ushered" into the River Humber.
After staying there until the bullies had gone, he went "dripping wet" to a nearby industrial area where a man wrapped him in a coat and placed him next to a heater, Hull Crown Court heard.
The teenager was taken to hospital after being hit at least twice by another youth, 17, and sustaining a cut to his mouth, reports Hull Live.
He had been punished after allegedly "grassing" on Kian Flaxman, 20, and the 17-year-old after his sister heard of a reward for information about a stolen motorcycle.
David Webster, prosecuting, said the victim was travelling in a Vauxhall Zafira car that was being driven by the 17-year-old with Flaxman and others as passengers. It had been stolen during a burglary in Hull.
The car stopped near an area of the River Humber before the teenager was prompted into the water, with Flaxman walking behind him to make sure he did not run away.
Mr Webster said: "He was then given no choice but to walk into the water at neck height. Even Flaxman says that it was chest height."
The teenager remained in the water for five minutes before he thought it was safe to get out.
The stolen car with Flaxman and the 17-year-old driver inside was later stopped by police after they used a tyre-bursting stinger.
The original charge concerning the incident with the 15-year-old boy was kidnap, the court heard.
In a separate robbery, Flaxman had targeted a 12-year-old boy who was using a mountain bike in a rough area of land.
While in a group, Flaxman blocked the boy's way so that he had to slam on the brakes and ended up being surrounded.
Flaxman then ordered the boy to get off his bike, the court heard, telling him: "Get off your bike, mush" in a menacing way.
Mr Webster said: "He felt that he had to comply. If he did not, he would be met with violence."
Flaxman rode off on his bike while wheeling the 12-year-old's bike - which cost £550 and had been given for his birthday just the day before - beside him.
Flaxman had convictions for 20 previous offences, including for dishonesty, and had been jailed for dangerous driving.
Stephen Robinson, mitigating, said the robbery involved "very unattractive bullying" and modest use of force.
He added: "It must have been very upsetting for him.
"The threat was repeated four or five times. He knew the complainant was younger than him but he did not appreciate quite how young. He appreciates that the victim will have been frightened by what happened."
Flaxman started committing offences because of upheaval in his family, the court heard.
"He is going to have to grow up fast," said Mr Robinson.
Flaxman's girlfriend was pregnant and, by being in custody, he would miss out on being able to help her and be with the baby.
Flaxman was sent to a young offenders' institution for two years.
Judge Mark Bury warned him to "stay away from bad influences" after his release from custody.
At an earlier hearing, the 17-year-old accomplice, who cannot be named, admitted assault and driving a car that had been taken without consent.
The youth was given a one-year youth rehabilitation order, including supervision, and was banned from driving for one year.
