A shopkeeper felt extreme fear when three men entered his Black Bull liquor store carrying hammers and a steel bar, later discovering one was his friend.
The offenders, whose identities were partially concealed, confronted the victim and threatened him before stealing cigarettes, alcohol and cash from the store.
They made their escape from Duncan St just after 9pm in a vehicle driven by a fourth male, but were tracked down and arrested by police using dog handlers.
Shakaia Rapana-Tuirirangi, 17, was a friend of the victim. He pleaded guilty to aggravated assault and was sentenced by Judge Philip Crayton in Whanganui District Court.
Judge Crayton said this type of offending happens far too often in Whanganui and stores such as Black Bull were seen as relatively easy targets.
"I don't think there is a week goes by without an aggravated robbery taking place in Whanganui and we are a town of 48,000 people," he said.
"There are so many. I come across people who have been victims time and time and time again."
Rapana-Tuirirangi's age, history, guilty plea, remorse shown, a cultural report about him and his 13 months on bail were all factors considered before sentencing.
The Judge said it was fortunate that there were no members of the public present at the time of the offending and that the victim was not injured.
Judge Crayton sentenced Rapana-Tuirirangi to 11 months' home detention and ordered him to pay $861.30 reparation.
"I hope that for your whānau and for you this is the last time we meet. You should be pretty grateful, you have got a lot of good support there," Judge Crayton said.
"I am grateful for all the support you have today. You need to acknowledge them and be thankful for it."
A co-offender, Tamehana Thompson has also pleaded guilty to aggravated robbery and will be sentenced on April 15. The other offender was Tangata Thomas-Paenui.