Judge Bridget Mackintosh said Broderick was a "talented sportsman", had performed well at school and the attack appeared "out of character". He had been a Hawke's Bay junior cricket representative.
Judge Mackintosh said there had been a "developmental block in the brain, which is apparent by this kind of conduct".
Despite Broderick landing the first hit of the attack when he kicked the electrician and left him "dazed and vulnerable", the judge said the beating was "probably fuelled by alcohol" and described it as a "brain explosion". References supporting Broderick's good character and remorse kept him out of jail, she said.
However, the victim, who was in the courtroom, was left in "total dismay and disbelief", his friend Ben Simmons said.
"He was obviously hoping for a very close sentence to [Walsh] because, in his mind, he considers it all part of the same action and the way they collaborated ... and left him there."
The electrician was unrecognisable following the attack and subsequently spent five days in hospital and 24 hours in an induced coma.
He had been celebrating a birthday with two friends who were in the village streets after the bars closed.
About 3.50am the two teens approached their victim, trying to "antagonise and wind him up", before Broderick said: "I should just smack him over."
Walsh punched him in the head up to seven times, until his knuckles bled.
Immediately after, Broderick and Walsh went to the Havelock North McDonald's, where they bragged openly about the beating.
"It's dangerous to say it's a brain explosion because going forward that's going to be every boozed-up kid's excuse for having a fight," Mr Simmons said.
The victim's sister said Broderick can walk away, and his life goes on, "but my brother's still recovering and still getting over what happened to him".
"I just feel really down and disappointed that it seems there is more rights for someone who can go out and do such a violent thing than there is for someone who will probably spend a lot longer recovering from such a horrible attack."
When Broderick left court he was welcomed by several family and friends.
As he was whisked away in a ute, Broderick made hand gestures out the window.
Sentence is 'a slap in the face'
Sensible Sentencing Trust spokesman Garth McVicar is appalled with the "pathetic sentence" given to Jacob Broderick.
Mr McVicar said it was an "absolute slap in the face" for the 33-year-old victim who continues to recover from the brutal Havelock North assault by Broderick and Falcon Walsh last year.
He said the sentence imposed on the 18-year-old yesterday of four months' community detention, 200 hours' community work and nine months' supervision escaped the "principles of sentencing".
"That sentence has no deterrent for future offending at all. That's supposed to be one of the principles of sentencing."
He said the sentencing judge, Bridget Mackintosh, had "given some of the most pathetic sentences this country has seen".
Hawke's Bay was dealing with some of the worst crime statistics in New Zealand and Mr McVicar said Broderick's sentence only adds to a "massive problem in society".
